Todd Graham is director of debate at Southern Illinois University. His teams have won national championships for three years, and he's been recognized twice as the national debate coach of the year. The opinions expressed in this commentary are his.

(CNN) I've often told my debate teams that we need more than criticisms of our opponents to win debates. We also need to present reasons for the judges not just to vote against our opponents, but also reasons for them to vote for us.

I'm grading the Thursday Republican debate based on both guidelines: Criticisms of opponents ("why the other guy shouldn't be president"), and reasons why we should vote for a particular candidate ("why you should vote for me").

John Kasich: B+

John Kasich took advantage of the strategy of two other debaters, Ted Cruz and Marco Rubio. He knew they'd attack Donald Trump, so he stayed out of the fray, even at one point saying, "I'm not biting" when asked to criticize Trump.

Kasich was able, once again, to be the adult in the room. As a strategy, this didn't succeed in previous debates when it wasn't such a Trump pile-on. That's because for the guidelines I mentioned above to work, Kasich would have had to show reasons to vote for him and reasons to vote against the other guy, which is Cruz and Rubio's new strategy.

But last night, it was if everything fell into place for Kasich. His theme for the night was the same as before (my accomplishments as a congressman and a governor), and he played it out over and over with examples of balancing the budget, cutting taxes and having the support of foreign policy experts. His argument: With Kasich, it's not a "theory," but a "reality."

Photos: John Kasich's political career Ohio Gov. John Kasich speaks at the First in the Nation Republican Leadership Summit on April 18, 2015, in Nashua, New Hampshire. The summit was attended by all the 2016 Republican candidates as well as those eying a run for the nomination. Click through for more on the political career of Kasich: Hide Caption 1 of 11 Photos: John Kasich's political career Kasich speaks during the Republican National Convention at the Tampa Bay Times Forum on August 28, 2012, in Florida. Hide Caption 2 of 11 Photos: John Kasich's political career Kasich, left, and then-Republican presidential candidate Mitt Romney talk with students during a roundtable discussion at Otterbein University on April 27, 2012 in Westerville, Ohio. Romney eventually won the 2012 GOP presidential nomination. Hide Caption 3 of 11 Photos: John Kasich's political career Kasich, left, President Barack Obama, center, and Republican House Speaker John Boehner play the first hole of a golf game on June 18, 2011, at Andrews Air Force Base in Maryland. Hide Caption 4 of 11 Photos: John Kasich's political career Kasich listens to Obama speak during a bipartisan meeting of governors hosted by the President and Vice President Joe Biden in the State Dining Room of the White House on February 28, 2010. Hide Caption 5 of 11 Photos: John Kasich's political career Before officially taking office as governor of Ohio, Kasich talks with reporters after meeting with House and Senate Republican leaders at the U.S. Capitol on December 1, 2010. The GOP leaders talked about ways to create jobs, cut spending and repeal the health care law. Hide Caption 6 of 11 Photos: John Kasich's political career Kasich, right, then a member of the U.S. House, sports "Bush" baseball caps with Texas Gov. George W. Bush on July 14, 1999. The two lawmakers held a news conference at the Ronald Reagan International Trade Center in Washington during Bush's presidential run. Kasich had previously announced that he was withdrawing from the 2000 presidential race and endorsed Bush. Hide Caption 7 of 11 Photos: John Kasich's political career U.S. Rep. Kasich delivers a speech in the Watergate complex in Washington on July 9, 1999, during the College Republican National Committee 53rd Biennial Convention. Other speakers included Republican 2000 presidential hopefuls such as Gary Bauer and Elizabeth Dole. Hide Caption 8 of 11 Photos: John Kasich's political career During a U.S. government shutdown, Kasich, left, and Sen. Pete Domenici, R-New Mexico, speak to reporters outside the White House on January 6, 1996. Hide Caption 9 of 11 Photos: John Kasich's political career Kasich shows a videotape of President Bill Clinton speaking during a news conference on Capitol Hill on December 16, 1995. Kasich was chairman of the House Budget Committee at the time and disputed Clinton's position on the budget. Hide Caption 10 of 11 Photos: John Kasich's political career Kasich, center, shows a thank you note in the form of a check to Speaker of the House Newt Gingrich, left, and Senate Majority Leader Robert Dole (right) on November 17, 1995, in Washington. They were soon engaged in bruising battles with President Bill Clinton over the federal budget. Hide Caption 11 of 11

By the way, this answers both of Trump's core arguments:

1) Politicians can't be trusted and accomplish nothing. Kasich disproved that with strong evidence of his own record as a successful politician.

And

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2) Flexibility is sometimes good. Kasich was better than Trump on this position, since he proved as governor that he has compromised to accomplish important goals, and that his flexibility, unlike Trump's, doesn't come at the cost of core Republican principles or flip-flopping. And Kasich added a new twist. He brought into the debate the notion of neighborhoods and working locally from the ground up. It is an approach to problems such as wages and education.

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So why the B+? He reversed his answer on commerce and sexual orientation. His previous answer was the slippery-slope argument that if we deny people service based on sexual orientation, then next up is divorced individuals, etc. Instead of defending this claim, Kasich instead took a hard right turn by stating that if a business doesn't do the right thing, "you shouldn't sue them."

In other words, if a business chooses to discriminate against the LGBT community or anyone, then the wronged party should just "take it," and the company should be allowed to discriminate whenever and however it pleases.

This wasn't just the opposite of his answer from the last debate, it was an outrageous answer to illegal discrimination. It says to voters that Kasich doesn't know what it's like to be discriminated against.

Ted Cruz: B-

Cruz's attacks were solid, but other than "I can win," he offered no solid reasons to vote for him, just reasons to vote against Trump. Still, it was going fine until Cruz whiffed on his "how to bring jobs to Detroit" question by first saying it was Obamacare's fault (as if Detroit was thriving before President Obama) and then by saying he'd stop Environmental Protection Agency regulations.

Photos: Moments from Ted Cruz's career U.S. Sen. Ted Cruz, a Republican presidential candidate, speaks during a campaign rally at the Indiana State Fairgrounds on Monday, May 2. Hide Caption 1 of 24 Photos: Moments from Ted Cruz's career Cruz holds up the hand of Carly Fiorina at a campaign rally in Indianapolis on Wednesday, April 27. Cruz named Fiorina, a former presidential candidate, as his running mate. Hide Caption 2 of 24 Photos: Moments from Ted Cruz's career Cruz celebrates his Wisconsin primary win with his wife, Heidi, and Gov. Scott Walker in Milwaukee on Tuesday, April 5. Walker endorsed Cruz for the presidency. Hide Caption 3 of 24 Photos: Moments from Ted Cruz's career With his wife by his side, Cruz tours the Dane Manufacturing facility before speaking to workers in Dane, Wisconsin, on Thursday, March 24. Hide Caption 4 of 24 Photos: Moments from Ted Cruz's career Cruz speaks during the CNN Republican debate in Miami on Thursday, March 10. Hide Caption 5 of 24 Photos: Moments from Ted Cruz's career Cruz and his wife wave to the crowd at Liberty University after he announced his presidential candidacy in Lynchburg, Virginia, on March 23, 2015. Hide Caption 6 of 24 Photos: Moments from Ted Cruz's career Cruz speaks during the 2013 NRA Annual Meeting and Exhibits at the George R. Brown Convention Center on May 3, 2013, in Houston, Texas. Hide Caption 7 of 24 Photos: Moments from Ted Cruz's career Cruz poses with his wife, Heidi, and his daughters Caroline and Catherine. Hide Caption 8 of 24 Photos: Moments from Ted Cruz's career Cruz (left) fields questions from Bruce Rastetter at the Iowa Ag Summit on March 7, 2015, in Des Moines, Iowa. The event allows the invited speakers, many of whom are potential 2016 Republican presidential hopefuls, to outline their views on agricultural issue. Hide Caption 9 of 24 Photos: Moments from Ted Cruz's career Nobel Peace Laureate Elie Wiesel (left) listens as Cruz (right) speaks during a roundtable discussion on Capitol Hill March 2, 2015 in Washington, D.C. Wiesel, Cruz and Rabbi Scmuley Boteach (center) participated in a discussion entitled 'The Meaning of Never Again: Guarding Against a Nuclear Iran.' Hide Caption 10 of 24 Photos: Moments from Ted Cruz's career Governor Greg Abbott (center) speaks alongside Cruz (left), Attorney General Ken Paxton (right) at a joint press conference February 18, 2015, in Austin, Texas. Hide Caption 11 of 24 Photos: Moments from Ted Cruz's career Sen. Patrick Leahy (right) escorts Loretta Lynch back from a lunch break as Cruz (left) sits nearby during her confirmation hearing before the Senate Judiciary Committee January 28, 2015, on Capitol Hill. Hide Caption 12 of 24 Photos: Moments from Ted Cruz's career Cruz greets supporters at the South Carolina Tea Party Coalition convention on January 18, 2015, in Myrtle Beach, South Carolina. A variety of conservative presidential hopefuls spoke at the gathering on the second day of a three-day event. Hide Caption 13 of 24 Photos: Moments from Ted Cruz's career Cruz (left) and then-Texas Governor Rick Perry stand together during a press conference at the front gate of Fort Hood about Iraq war veteran, Ivan Lopez, who killed three and wounded 16 before taking his own life on April 4, 2014, in Fort Hood, Texas. Hide Caption 14 of 24 Photos: Moments from Ted Cruz's career (Left to right) Sen. Lindsey Graham, Sen. John McCain and Cruz listen as President Barack Obama delivers the State of the Union address on January 28, 2014, in Washington, D.C. Hide Caption 15 of 24 Photos: Moments from Ted Cruz's career Then-Senate Minority Leader Mitch McConnell (second right), poses with Republican senators-elect Jeff Flake (left), Deb Fischer (second left), and Cruz (right) at the U.S. Capitol on November 13, 2012, in Washington, D.C. Hide Caption 16 of 24 Photos: Moments from Ted Cruz's career Cruz speaks to reporters on September 25, 2013, after ending his talk-a-thon on the floor of the US Senate in Washington, D.C. Hide Caption 17 of 24 Photos: Moments from Ted Cruz's career Cruz speaks as then-Rep. Michele Bachmann (left), Sen. Mike Lee (second right) and Sen. Rand Paul (right) listen during a news conference May 16, 2013, on Capitol Hill. Hide Caption 18 of 24 Photos: Moments from Ted Cruz's career Cruz listens to testimony during a Senate Judiciary Committee hearing on April 22, 2013, in Washington, D.C. Hide Caption 19 of 24 Photos: Moments from Ted Cruz's career Cruz holds a news conference to announce the plan to defund Obamacare on March 13, 2013. Hide Caption 20 of 24 Photos: Moments from Ted Cruz's career Cruz speaks at the CPAC on March 6, 2014, in National Harbor, Maryland. Hide Caption 21 of 24 Photos: Moments from Ted Cruz's career Then-Senate Republican Candidate and Texas Solicitor General Cruz speaks at the 'Patriots for Romney-Ryan Reception' on August 29, 2012, in Tampa, Florida. Hide Caption 22 of 24 Photos: Moments from Ted Cruz's career Then-Senate Republican Candidate and Texas Solicitor General Cruz speaks during the Republican National Convention at the Tampa Bay Times Forum on August 28, 2012. Hide Caption 23 of 24 Photos: Moments from Ted Cruz's career Then-Senate Republican Candidate and Texas Solicitor General Cruz speaks during the Republican National Convention in 2012. Hide Caption 24 of 24

That's a terrible answer to a jobs question in Detroit. All we need to do is think about Flint, lead poisoning and the role of a stronger (not weaker) EPA. Cruz's generic "jobs" answer to a specific question about Detroit wasn't fitting.

Marco Rubio: C+

Great attacks on Trump. He convinced people in this debate that Trump isn't ready to be president with his sustained criticism of Trump University and ethics, Trump's lack of specifics and Trump's name-calling.

However, I never heard a reason why Rubio would be the right choice for president. His debating technique was skewed too far toward criticizing Trump and not enough toward describing why America would succeed under Rubio.

Photos: Moments from Marco Rubio's career Florida Sen. Marco Rubio speaks in October 2013 at the Values Voter Summit, held by the Family Research Council in Washington. Hide Caption 1 of 20 Photos: Moments from Marco Rubio's career Sen. Mike Lee, left, and Rubio talk before a news conference to introduce their proposal for an overhaul of the tax code in March. Hide Caption 2 of 20 Photos: Moments from Marco Rubio's career Rubio, center, arrives in the House chamber ahead of Israeli Prime Minister Benjamin Netanyahu's address to a joint meeting of the U.S. Congress in March. Hide Caption 3 of 20 Photos: Moments from Marco Rubio's career Rubio speaks with the media after delivering remarks during the graduation of small business owners from the Goldman Sachs 10,000 Small Businesses program held in Miami in February. Hide Caption 4 of 20 Photos: Moments from Marco Rubio's career Rubio talks to aides in December before speaking on President Barack Obama's announcement about revising policies on U.S.-Cuba relations. Hide Caption 5 of 20 Photos: Moments from Marco Rubio's career Rubio, left, talks to Sen. Lindsey Graham prior to a news conference on Capitol Hill in July. Hide Caption 6 of 20 Photos: Moments from Marco Rubio's career Rubio talks to reporters in June after a closed door briefing on Capitol Hill. Hide Caption 7 of 20 Photos: Moments from Marco Rubio's career Rubio speaks to the media in front of a wall dedicated to the victims of the violence in Venezuela as he shows support for the Venezuelan community at a restaurant in Doral, Florida, in April 2014. Hide Caption 8 of 20 Photos: Moments from Marco Rubio's career Rubio speaks to the media at the Doral restaurant in April 2014. Hide Caption 9 of 20 Photos: Moments from Marco Rubio's career Rubio checks his phone in March as he arrives for a Capitol Hill news conference to introduce a proposal for an overhaul of the tax code. Hide Caption 10 of 20 Photos: Moments from Marco Rubio's career Rubio, left, is greeted as he arrives at a restaurant in Doral in February 2014. Hide Caption 11 of 20 Photos: Moments from Marco Rubio's career Rubio, left, and Florida Gov. Rick Scott speak to the media in Doral in February 2014. Hide Caption 12 of 20 Photos: Moments from Marco Rubio's career From left, Sens. Cory Booker, Rubio, Kristen Gillibrand and John McCain wait for Obama to deliver the State of the Union address in January 2014. Hide Caption 13 of 20 Photos: Moments from Marco Rubio's career Rubio addresses an event held by the American Enterprise Institute for Public Policy Research in January 2014. Hide Caption 14 of 20 Photos: Moments from Marco Rubio's career Paralympian Brad Snyder poses with Rubio during a Team USA Congressional visit in November 2013. Hide Caption 15 of 20 Photos: Moments from Marco Rubio's career Rubio speaks in November 2013 during a campaign stop for Virginia Attorney General Ken Cuccinelli, the Republican candidate for governor of Virginia. Hide Caption 16 of 20 Photos: Moments from Marco Rubio's career Rubio confers with McCain as U.S. Ambassador to Syria Robert Ford testifies before the Senate Foreign Relations Committee in October 2013. Hide Caption 17 of 20 Photos: Moments from Marco Rubio's career Rubio, center, speaks to members of the media as Sen. Ron Johnson, left, and Rep. Ron DeSantis listen during a news conference on Capitol Hill in October 2013. Hide Caption 18 of 20 Photos: Moments from Marco Rubio's career Rubio returns to the Capitol after meeting with Obama and other Republican leaders about the government shutdown in October 2013. Hide Caption 19 of 20 Photos: Moments from Marco Rubio's career Rubio speaks to an aide on Capitol Hill as he arrives for the weekly Senate Republican Policy Committee luncheon in September 2013. Hide Caption 20 of 20

Donald Trump: F

Remember, I'm judging this debate, and this debate only. If people knew nothing about Trump but what they learned from this debate, he'd have no chance to win the Republican nomination. None. Rubio said he wasn't "intellectually curious" enough on the issues to be president. In other words, Trump isn't bright.

Trump did nothing to dispel this notion in the debate.

Photos: Donald Trump in the public eye Business mogul Donald Trump announces his candidacy for the U.S. presidency at Trump Tower on Tuesday, June 16, 2015, in New York City. Hide Caption 1 of 21 Photos: Donald Trump in the public eye Donald Trump attends golf legend Jack Nicklaus' Congressional Gold Medal ceremony on March 24, 2015, in the U.S. Capitol Rotunda. Trump announced on March 18 that he had launched a presidential exploratory committee. Hide Caption 2 of 21 Photos: Donald Trump in the public eye Trump speaks to guests at the Iowa Freedom Summit on January 24, 2015, in Des Moines, Iowa. Hide Caption 3 of 21 Photos: Donald Trump in the public eye As chairman and president of the Trump Organization and the founder of Trump Entertainment Resorts, Trump speaks during day two of the Republican Leadership Conference on May 30, 2014, in New Orleans. Hide Caption 4 of 21 Photos: Donald Trump in the public eye Former U.S. vice presidential candidate and Alaska Gov. Sarah Palin and Trump walk toward a limousine after leaving Trump Tower, at 56th Street and Fifth Avenue, on May 31, 2011, in New York City. Hide Caption 5 of 21 Photos: Donald Trump in the public eye Trump looks out the window of his limousine after visiting Newick's Lobster House on April 27, 2011, in Dover, New Hampshire. Hide Caption 6 of 21 Photos: Donald Trump in the public eye Trump speaks to the media at Pease International Tradeport on April 27, 2011, in Portsmouth, New Hampshire. Hide Caption 7 of 21 Photos: Donald Trump in the public eye Trump speaks to a crowd at the Palm Beach County Tax Day Tea Party on April 16, 2011, at Sanborn Square in Boca Raton, Florida. Hide Caption 8 of 21 Photos: Donald Trump in the public eye Trump and his wife, Melania, attend the Michael Kors Spring 2011 fashion show during Mercedes-Benz Fashion Week at The Theater at Lincoln Center on September 15, 2010, in New York City. Hide Caption 9 of 21 Photos: Donald Trump in the public eye Trump kisses Miss Universe 2009 Stefania Fernandez as they arrive at the 2010 Miss Universe Pageant at the Mandalay Bay Events Center on August 23, 2010, in Las Vegas. Hide Caption 10 of 21 Photos: Donald Trump in the public eye Trump and his children Eric (second from left), Ivanka and Donald Jr. attend the ribbon-cutting ceremony for Trump SoHo New York at Trump SoHo on April 9, 2010, in New York City. Hide Caption 11 of 21 Photos: Donald Trump in the public eye Trump, his daughter Ivanka, wife Melania and son Barron attend the "The Trump Card: Playing to Win in Work and Life" book launch celebration at Trump Tower on October 14, 2009, in New York City. Hide Caption 12 of 21 Photos: Donald Trump in the public eye Trump and professional tennis player Serena Williams attend the Gucci cocktail party for the Foundation For the Advancement of Women Now at Gucci Fifth Avenue on September 16, 2009, in New York City. Hide Caption 13 of 21 Photos: Donald Trump in the public eye Trump and his wife, Melania, left, attend the launch of Trump International Hotel and Tower Dubai with model Heidi Klum on June 23, 2008, at the Park Avenue Plaza in New York City. Hide Caption 14 of 21 Photos: Donald Trump in the public eye Trump attends the debut of a Lego replica of the Trump International Hotel & Tower Dubai on June 23, 2008, at Central Park in New York City. Hide Caption 15 of 21 Photos: Donald Trump in the public eye Trump attends the announcement of a partnership with Affliction Entertainment on June 5, 2008, at Trump Tower in New York City. Hide Caption 16 of 21 Photos: Donald Trump in the public eye Trump attends the Donald Trump Friars Club Roast Luncheon at the New York Hilton on October 15, 2004, in New York City. Hide Caption 17 of 21 Photos: Donald Trump in the public eye Trump poses with the new Donald Trump 12-inch talking doll on September 29, 2004, at the Toys 'R' Us store in New York City. Hide Caption 18 of 21 Photos: Donald Trump in the public eye Trump arrives at "The Apprentice" casting call in Trump Tower on July 30, 2004, in New York City. Hide Caption 19 of 21 Photos: Donald Trump in the public eye Trump dips Marla Maples after the couple married in a private ceremony amid tight security at the Plaza Hotel on December 20, 1993, following a six-year courtship. Hide Caption 20 of 21 Photos: Donald Trump in the public eye Trump and his wife, Ivana, arrive at a social engagement on December 4, 1989, in New York. Hide Caption 21 of 21

He provided no answers on myriad issues, from foreign policy; to why the military would follow him when he asks it to violate international law (because I say so, was his alarming answer); to his double standard on trade (talks tough while hiring foreign workers); to how he accounts for the $10 trillion debt his plan would produce, by some accounts (Chris Wallace had slides, for goodness sake); to his multiple flip-flops in these areas: deportation, visas, Syrian refugees, Afghanistan War, whether Bush "lied," If he's friend or foe to Russian President Vladimir Putin.

Trump came across as less trustworthy than in previous debates, not because he's "flexible," but because he did not seem as clearly defined compared with previous debates. His primary debating strategy was to call Rubio and Cruz names -- no surprise there.

But his biggest failure was that he lacked any persuasive reason for why Republicans should vote for him.