Count the swipes Republican presidential candidates Marco Rubio and Donald Trump took at each other the day after they butted heads at the Houston CNN/Telemundo debate. (Sarah Parnass/The Washington Post)

Hours after mounting the fiercest assault of his campaign against Donald Trump in Thursday’s debate, Marco Rubio established a new line of attack against the Republican front-runner, branding him a “con artist” and hurling insult after insult at him during a Friday morning rally in Dallas.

Rubio mocked Trump’s misspelled tweets. He jabbed at Trump’s age. And he portrayed Trump as a scared and phony politician.

On social media, Trump launched his own offensive, labeling Rubio “Mr. Meltdown” and pointing to his spotty Senate attendance record. And Trump won the endorsement of New Jersey Gov. Chris Christie, the ex-candidate who waged a bruising attack against Rubio at a debate in New Hampshire.

The dramatic escalation in hostility between two candidates, who had mostly avoided each other before the debate, set the stage for a brutal 2 1/2-week stretch that appears set to determine whether Trump will effectively clinch the Republican nomination by mid-March or whether the race will drag on, possibly all the way to the GOP convention in July.

Things got downright personal at the Feb. 25 GOP debate. Here are a few of the most stinging barbs thrown by Donald Trump, Ted Cruz and Marco Rubio. (Peter Stevenson/The Washington Post)

A third candidate, Sen. Ted Cruz (Tex.), who struggled at times to edge himself into the conversation Thursday night in Houston, embarked on an ambitious campaign schedule as he battled with Rubio to be seen as the chief alternative to Trump.

In essence, Rubio is trying to beat Trump at his own game, lobbing memorable one-liners designed to attract widespread attention. He is also going after Trump’s business background, a cornerstone of his pitch to voters.

In Dallas, Rubio gleefully pulled out his smartphone and read aloud some of Trump’s misspelled attack tweets. He said he could draw only two conclusions about why Trump messed them up.

“Number one: That’s how they spell those words at the Wharton School of Business, where he went. Or number two, just like Trump Tower, he must have hired a foreign worker to do his own tweets,” quipped Rubio.

Rubio, 44, also highlighted the age gap between him and Trump, 69.

“He would be the oldest president ever elected. And it’s like an eight-year term, so you start to worry,” said Rubio.

The Florida senator said Trump requested a full-length mirror during a break in the debate, “maybe to make sure his pants weren’t wet.” And he questioned Trump’s toughness by charging that he was “the first guy that begged for Secret Service protection.”

Rubio is also trying to draw a contrast between his readiness to be commander in chief and Trump’s. Stoking doubts about Trump’s leadership, Rubio said on CBS that a Trump administration “would be chaos,” and “nobody knows” what it would look like.

Meanwhile, a super PAC supporting Rubio released new TV ads Friday that will air in March states. One argues Rubio is an “expert” on foreign policy while Trump “knows nothing” about it. The other claims Trump “puts himself first and us last.”

In Thursday’s debate, Rubio swung hard at Trump from the opening moments. He accused the billionaire real estate developer of hiring foreign labor over Americans and offering few specifics on health-care policy.

He also took personal shots at Trump, memorably charging that Trump would be “selling watches in Manhattan” if he had not received a generous inheritance.

For Rubio, it marked a sharp departure from months of mostly sidestepping Trump and expressing distaste for personal attacks. It also reflected the urgency of his task. Trump is on a three-state winning streak and leads in the polls in a slate of “Super Tuesday” states holding nominating contests on March 1. Rubio has yet to win a state, and his aides are not predicting victory anywhere on Tuesday.

The one state where they are predicting victory is Rubio’s home state of Florida on March 15, where a Quinnipiac University poll released Thursday showed Trump leading Rubio by 16 points.

“Why would the people of Florida vote for Marco Rubio when he defrauded them by agreeing to represent them as their Senator and then quit!” Trump tweeted Friday. Rubio has taken heat for missing many Senate votes. A 2015 study by Vocativ and Govtrack found Rubio to be the most absent member of the Senate.

To his more than 6 million Twitter followers, Trump lashed out at both Rubio and Cruz, firing off a string of insults that contained some spelling errors.

“Lightweight Marco Rubio was working hard last night. The problem is, he is a choker, and once a choker, always a chocker! Mr. Meltdown,” read one tweet.

Later, he predicted a “big crowd” at a midday rally in Fort Worth, and promised he would “be talking about the debate.”

“Lying Ted Cruz and lightweight choker Marco Rubio teamed up last night in a last ditch effort to stop our great movement. They failed!” he added in a subsequent tweet.

In the debate, Trump referred to Rubio as a “choke artist,” pointing to his widely panned debate performance in New Hampshire, where Christie mocked him for coming across as too scripted and robotic to devastating effect.

Christie appeared with Trump on Friday in Fort Worth, Tex. In a statement, he called Trump “a leader” who is not “afraid to tell it like it is.”

Trump has taken the lead in the battle for delegates after decisive wins in New Hampshire, South Carolina and Nevada. A good showing on Tuesday could put him in even stronger position, leading some detractors to fear that his opponents have waited too long to wage a full-fledged strike against him.

Two weeks later on March 15, Florida and Ohio will be among the states voting. Unlike the earlier states, they will award their delegates on a winner-take-all basis. The prospect of quickly eating into Trump’s lead that day has kept hope alive for Rubio backers. It has also raised the hopes of Ohio Gov. John Kasich, a centrist candidate who has shown no signs he plans to drop out before his home state votes.

Rubio and his campaign have said that a contested convention is one possible outcome they are preparing for. If no one wins a majority of delegates, the fight would culminate in Cleveland in July.

Rubio, Cruz and Trump planned to spend Friday and the weekend focusing on states voting on March 1.

In addition to Dallas, Rubio also intends to stump in Oklahoma City on Friday. He plans to hold events Saturday in Georgia, Arkansas and Alabama.

Trump’s Friday schedule looked similar. He planned to hold rallies in Fort Worth and then Oklahoma City. He is scheduled to be in Arkansas and Tennessee on Saturday.

Cruz planned to be in Nashville and Virginia Beach on Friday, focusing on March 1 states as well. He will spend Tuesday night in his home state, where he desperately needs to win after three consecutive third-place finishes.

Cruz accused Trump of being insufficiently conservative at Thursday’s debate, continuing a fight he has been waging throughout the early state contests. Cruz defeated Trump and the rest of the field in Iowa.

“He is promising if he’s elected he will go and cut deals in Washington. And he’s right. He has supported — he has given hundreds of thousands of dollars to Democrats. Anyone who really cared about illegal immigration wouldn’t be hiring illegal immigrants,” Cruz said.

Trump called Cruz a “basket case” and pointed to the disdain many of his Senate colleagues have for him.

After the debate, Cruz said in an interview with CNN that he and Rubio are “friends,” but he cast him disparagingly as a latecomer to the struggle against Trump.

“He did something tonight that he’s never done, which is he actually for the first time took on Donald Trump. And I’m glad he did,” Cruz said.

Karen Tumulty and Robert Costa in Houston contributed to this report.