 -- NOTABLES

--TRUMP -- 'VERY SERIOUSLY' CONSIDERING SUING TED CRUZ: Republican presidential front-runner Donald Trump says he is "very seriously" considering suing GOP rival Sen. Ted Cruz over recent comments about his record. "I’m thinking about it very seriously," Trump told ABC’s GEORGE STEPHANOPOULOS on "Good Morning America" today. "I’ve never dealt with anybody who lies like him." Trump pointed to his own positions on gun rights, as well as the dismantling President Obama's signature health care law, saying that the Texas senator was misleading voters about his stances, according to ABC’s RYAN STRUYK. http://abcn.ws/1PYALcq

--ANALYSIS -- ABC’s RICK KLEIN: If Donald Trump captures the Republican Party’s nomination, the party itself will almost need a new name. He’s not running for the GOP but against it – against the party’s formal structure, its biggest players, and, yes, some of its core values. Consider his actions just since this past weekend. Trump is accusing the Republican Party of breaking its pledge to treat him fairly, in an implicit threat of a third-party run; saying that the GOP’s most-recent, two-term president tied the nation into a war; mocking the two leading establishment candidates, Jeb Bush and Marco Rubio, for energy level and propensity to perspire, respectively; and calling his leading rival, Ted Cruz, “very unstable” and the biggest liar he’s ever come into contact with. The biggest shocker is that Trump might win South Carolina and much more because of such statements, not in spite of them. For those who have come up under existing power structures – and that list includes Bush, Rubio, Cruz, and John Kasich – Trump’s continued strength is confounding, dangerous, and yet very much reality.

--BUSH BROS MAKE JOINT PITCH TO SOUTH CAROLINA VOTERS: In his first public campaign event on behalf of his brother, former President George W. Bush told South Carolinians that “there is no doubt in my mind that Jeb Bush has the experience and the character to be a great president.” “The presidency is a serious job that requires sound judgment and good ideas,” the former president said, assuring the crowd that he was appearing here for two reasons. “One, because I care deeply about Jeb,” he said, “and two, because I care deeply about our country.” ABC’s CANDACE SMITH notes that the event, at an arena just north of Charleston, was the largest since Jeb Bush announced his presidential bid. The former president made a forceful case for his brother, whose candidacy has yet to catch fire, offering, at times, a deeply personal assessment of his sibling’s qualifications for the White House. “Jeb is a man of humble, deep and genuine faith,” the former president said. “Faith that reveals itself through good works, not loud words.” http://abcn.ws/1Wo6CDv

--WHAT JEB SAID: In his remarks last night, Jeb, who the former president introduced as his "little, big brother," took on Donald Trump’s attacks on him and his family at Saturday night’s Republican presidential debate. “I thought it was a little strange that a front-running candidate would attack the President of the United States who did keep us safe while he was building a reality TV show,” Jeb Bush said. (At the debate, Trump pointed out that "the World Trade Center came down during your brother's reign.")

--W. GOT THE TALKING POINTS: He seriously did: “The presidency is a serious job that requires sound judgment and good ideas,” the former president said, adding: “This is a serious election for a serious job.” And introducing Jeb: “Please welcome a serious and thoughtful candidate, a good man. A man I am proud to call my big little brother, Jeb Bush.”

HAPPENING TODAY IN THE PALMETTO STATE: CRUZ TO UNVEIL MILITARY PLAN. In The Note’s inbox from the Cruz campaign: “Today, Presidential candidate Ted Cruz will unveil his plan to rebuild our military and ensure the United States has the resources it needs to protect our vital national security interests and maintain its position as a beacon of freedom to the rest of the world. He will be joined by former Texas Governor and U.S. Air Force veteran Rick Perry.” The event takes place at 10:00 a.m. ET aboard the USS Yorktown in Mt. Pleasant, South Carolina.

YESTERDAY ON THE TRAIL with ABC’s PAOLA CHAVEZ and VERONICA STRACQUALURSI

TRUMP CALLS CRUZ A ‘LIAR’ AND ‘UNSTABLE,’ THREATENS TO SUE HIM. Donald Trump called Sen. Ted Cruz an "unstable person" and a "liar" and threatened to sue him over his eligibility to be president if he didn't "take down his false ads and retract his lies" in recent statements. ABC’s VERONICA STRACQUALURSI reports, Trump accused Cruz of having "printed lies" about his record in recent advertisements and statements regarding his position on abortion, the Second Amendment and whether or not he would pick liberal judges to replace Justice Antonin Scalia's vacant seat on the Supreme Court. http://abcn.ws/1Tjxt4g

--WHAT CRUZ IS SAYING: Cruz blasted Trump in an event yesterday -- saying that the business mogul "apparently lost it" at his press conference. “I think the people of South Carolina deserve a campaign focused on issues, and substance, and record. But I will continue pointing out the truth about records,” Cruz told an enthusiastic crowd in Camden, South Carolina. “It is not a response simply to start yelling louder and louder ‘liar, liar, liar’ whenever anyone points to the candidate’s own record. Truth matters. And we are not in grade school where you just get to say ‘liar, liar, pants on fire’ and not respond to the substance.” The senator offered a dig at Trump saying the only explanation for Trump's presser must be that his "internal poll numbers in South Carolina must be plummeting following that debate," ABC’s JEFF NAFT and JESSICA HOPPER note. "The stakes are too serious for continuing like it's a circus," he also said. http://abcn.ws/1Tjxt4g

TRUMP FLOATS IDEA OF A THIRD-PARTY RUN (AGAIN). At a town hall Monday in Mount Pleasant, South Carolina, Donald Trump floated the idea -- without explicitly threatening to do so -- that he may run as an independent candidate. According to ABC’s BRAD MIELKE, Trump attacked the Republican National Committee, saying it "better get its act together" and it "does a terrible job." Trump said he believes the RNC treated him unfairly. http://abcn.ws/1TjkKig

BILL CLINTON TELLS TRUMP SUPPORTER TO ‘FOLLOW HIM LIKE MOSES TO THE PROMISE LAND’. At a capacity campaign event in Riviera Beach, Florida, Bill Clinton played campaign surrogate again for his wife, Hillary Clinton, but this time he was in Donald Trump’s backyard, just next door to West Palm Beach. The former president was in his usual stump when a man in the crowd took off his shirt, revealing a concealed Donald Trump t-shirt. ABC’s MATTHEW CLAIBORNE reports the man waved a Trump campaign sign back and forth and bellowed in protest, “You took his money!” The crowd booed the protester and held up competing Hillary Clinton campaign signs that read, “You can’t make America great with hate,” a clear jab at Trump. http://abcn.ws/1Wo46NL

IN CASE YOU MISSED IT

CLINTON BARKS LIKE A DOG WHILE CONDEMNING REPUBLICANS. Hillary Clinton got unusually riled up at a rally in Reno, Nevada, Monday. So much so that she barked like a dog. The unexpected moment occurred while Clinton was telling a story about fact-checking Republicans, whom she accused of twisting the truth about the Great Recession, ABC’s LIZ KREUTZ writes. Clinton explained that it reminded her of an old radio ad she liked in Arkansas where a dog would bark every time a candidate said something that wasn’t true. “The dog was barking on the radio and so people were barking at each other for days after that,” Clinton said. "I want to figure out how we can do that with Republicans.” http://abcn.ws/1Wofmtm

WHO’S TWEETING?

@edatpost: NEW THIS MORNING: How the war in Iraq is haunting the 2016 presidential contest http://wpo.st/MUFC1 (w/ @agearan)

@EliStokols: Anyone else up 20 w/ 5 days to go plays it safe. But when your strategy is dominating earned media, you attack. http://www.politico.com/story/2016/02/trump-ted-cruz-dishonest-219301#ixzz40GNiJhOV …

@RobSaliterman: Right to Rise taking it to Trump everywhere. Just saw their anti-Trump ad on MSNBC in Manhattan.

@aebrandenburger: Jeb Bush was 1st candidate to file a full list of delegates & alternates & the fee for the Idaho primary, submitted 46 names. Deadline 2/22

@bgittleson: Fun fact: John Kasich's final event of the day was at a former Dress Barn in a shopping center in Utica, MI