(CNN) Senator Lindsey Graham is ending his presidential campaign, he told CNN during an exclusive interview airing Monday.

"I'm going to suspend my campaign. I'm not going to suspend my desire to help the country," the South Carolina senator said in a wide-ranging and candid discussion in which he acknowledged: "I've hit a wall here."

He made the official announcement in an email to supporters and Youtube video posted Monday morning.

Graham is known for his quick wit and famous for his one-liners (just ask Princess Buttercup about his retort from the last debate), but he was sober, serious and emotional as he described his decision to leave the race just weeks before the voting begins.

One thing is clear: Graham still wants his voice heard on the direction his party is headed, especially with regard to the Middle East.

"Here's what I predict. I think the nominee of our party is going to adopt my plan when it comes time to articulate how to destroy ISIL," he said. "We've fallen short here, but the fight continues. To those who are doing the fighting, I want to be your voice. To those in the Republican Party who want to win, check my plan out. Hillary, if you get to be President, I'll help you where I can. I hope you're not. But if you are, I'll be there to help you win a war we can't afford to lose."

Graham's decision -- which leaves a field of 12 main GOP candidates (CNN had 13 at its last Republican debate, including Graham) -- comes just days after the CNN Republican Presidential Debate in Las Vegas, where he was widely viewed as dominating the undercard debate.

"Four months ago at the very first debate, I said that any candidate who did not understand that we need more troops on the ground in Iraq and Syria to defeat ISIL was not ready to be Commander in Chief," Graham wrote in the email. "At the time, no one stepped forward to join me. Today, most of my fellow candidates have come to recognize this is what's needed to secure our homeland."

He added, "While we have run a campaign that has made a real difference, I have concluded this is not my time."

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"My biggest problem is a lot of people like what I say, but not a lot of people hear it," he told CNN. "I don't want to be the undercard voice. I cannot tell you how frustrating it has been to have spent all this time and effort preparing myself to be Commander-in-Chief and to be put at the 'kiddie table'." His advice to his party as it relates to the debate format: "Never do this again."

Graham's campaign strategy had been laser-focused on New Hampshire: Place high in that first primary state on February 9 and use the momentum to propel him forward. So why not hold out until then?

Photos: Lindsey Graham's political career Photos: Lindsey Graham's political career Click through to see highlights from U.S. Sen. Lindsey Graham's political career: Hide Caption 1 of 14 Photos: Lindsey Graham's political career Graham; Sir Elton John, center; and filmmaker and John's husband, David Furnish, pose after testimony at a U.S. Senate hearing on the global fight against AIDS on May 6, 2015. Graham and Democratic Sen. Patrick J. Leahy of Vermont hosted John as part of their bipartisan effort to combat HIV infection. Hide Caption 2 of 14 Photos: Lindsey Graham's political career Graham rushes to the Senate chamber to vote on an attempt to override U.S. President Barack Obama's veto of the Keystone XL Pipeline legislation March 4, 2015. Graham was elected to the U.S. Senate in 2002 and was re-elected in 2008 and 2014. Hide Caption 3 of 14 Photos: Lindsey Graham's political career Graham listens to testimony during a Senate Armed Services Committee meeting on national security strategy on January 27, 2015. According to his website , Graham continues to serve his country in the U.S. Air Force Reserves as a senior individual mobilization augmentee to the judge advocate general. Hide Caption 4 of 14 Photos: Lindsey Graham's political career Graham arrives for a closed briefing of the Armed Services Committee on July 30, 2014. Before serving in the Senate, Graham was elected to the U.S. House of Representatives in 1994. Hide Caption 5 of 14 Photos: Lindsey Graham's political career Graham talks to U.S. Sen. Marco Rubio, R-Florida, before a news conference on Capitol Hill on July 24, 2014. Hide Caption 6 of 14 Photos: Lindsey Graham's political career Graham and U.S. Sen. Ted Cruz, R-Texas, right, listen as President Barack Obama delivers the State of the Union address on January 28, 2014. Graham was in the U.S. Air Force and logged six-and-a-half years of service on active duty as an Air Force lawyer. Hide Caption 7 of 14 Photos: Lindsey Graham's political career Graham holds a news conference on Benghazi, Libya, at the U.S. Capitol on October 30, 2013. From left, he is flanked by Sen. John McCain, R-Arizona; Rep. Jason Chaffetz, R-Utah; and Rep. Jim Jordan, R-Ohio. Graham has been an outspoken critic of how the Obama administration has handled the September 11, 2012, attack on the U.S. diplomatic, in which four U.S. citizens died. Hide Caption 8 of 14 Photos: Lindsey Graham's political career Israeli Prime Minister Benjamin Netanyahu, center, meets with U.S. Sen. John McCain, R-Arizona, and Graham on June 30, 2013, in Jerusalem. Hide Caption 9 of 14 Photos: Lindsey Graham's political career McCain, left, and Graham speak during a news conference about Benghazi on February 14, 2013, on Capitol Hill. Hide Caption 10 of 14 Photos: Lindsey Graham's political career Graham talks with reporters before heading into the Senate Republican Caucus policy luncheon at the U.S. Capitol May 8, 2012. Hide Caption 11 of 14 Photos: Lindsey Graham's political career Graham speaks to reporters after a news conference about his Social Security reform plan at the U.S. Capitol on April 13, 2011. Hide Caption 12 of 14 Photos: Lindsey Graham's political career Graham, left, and McCain call on participants during a health care town hall meeting on September 14, 2009 at the Citadel in Charleston, South Carolina. According to his website, Graham is a native South Carolinian and grew up in a blue collar family in the small town of Central, where his parents ran a restaurant and pool hall. Hide Caption 13 of 14 Photos: Lindsey Graham's political career U.S. President George W. Bush, left, stands with Graham on the steps of Air Force One at the airport in Greenville, South Carolina, in March 2002. Hide Caption 14 of 14

"I'm not trying to hold out. I'm trying to make a difference. I think the best way for me to make a difference is to think about helping somebody else," he said.

In another key primary state, South Carolina, he faces a Monday December 21 deadline to keep his name off the ballot, potentially helping Graham avoid an embarrassing showing in his home state. Asked whether that fueled his decision to drop out now, Graham said no and added that he'd risk it if he saw a way to turn things around.

"At the end of the day, I'm not going to be competitive in my state," he said. "I'm not going to be competitive outside my state."

Asked who he would endorse, Graham demurred. "I'm going to take some time with my family. Going to think about what I should do. I have no intention of endorsing anyone right now." Later, he said that if he were to endorse, he's looking for the candidate best fit to be Commander-in-Chief and also who can win.

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As for the candidate Graham has traded barbs with the most since he entered the race in early June, Graham struck a markedly softer tone toward Donald Trump."You're doing really well. I'm impressed with your campaign," he said.

Graham -- who recently urged Republicans to tell Trump to " go to hell " -- also did not rule out accepting a Cabinet position in a Trump administration in the future.

But he did offer these parting words for Trump: "We're at war. A lot of men and women are at risk overseas. Watch what you say over here."

"You may wind up being the nominee of the Republican Party," he added. "The Republican Party's future may be in your hands. The future of the country will be in your hands if you're President of the United States. This is not a game show. This is not a reality show."

Candidly, Graham said he has a lot of regrets looking back at his campaign. "I regret that I haven't been a better candidate. I regret that I never got on the big stage. I regret that I didn't make it to the final group. But that's just about me. I have no regrets about running for President," he said. "It has been the joy of my life to run for President of the United States."