New Jersey Gov. Chris Christie’s endorsement Friday of GOP presidential candidate Donald Trump was a setback to rival Sen. Marco Rubio, but only the beginning.

Christie made the endorsement at a Trump campaign rally in Texas. And he’s back on the stump Saturday in Arkansas and Tennessee, where he’s expected to fulfill the role of political attack dog.

The tough-talking Christie dropped out of the GOP presidential race after a poor finish in the Feb. 9 New Hampshire primaries but not before a visceral debate attack on Rubio that put the Florida senator and his campaign on the ropes.

“I will lend my support between now and November in every way that I can,” Christie said in endorsing Trump in Fort Worth, Texas.

Christie largely stuck with the argument that Trump is “the best person ... undoubtedly” to beat Democratic front-runner Hillary Clinton.

However, he also argued that Rubio and Texas GOP Sen. Ted Cruz, Trump’s other biggest challenger ahead of the Super Tuesday primaries in three days, are “junior senators” for whom Clinton has a “standard political playbook” to defeat them.

Christie made the endorsement the day after Rubio's best debate performance, muting his long-awaited and damaging attacks against billionaire businessman Trump on such issues as immigration, foreign policy and hiring practices.

“The biggest damage to Rubio is he may be losing what should have been a major news cycle for him,” Joe Desilets, a Republican strategist and managing partner at the Washington firm 21st & Main, told FoxNews.com on Saturday. “On the trail, Donald Trump now has his first mainstream surrogate, and one that has already proven he can get to Rubio.”

However, he thinks Christie is largely acting in self-interest, likely trying to advance his political career if Trump wins the presidency.

“Rubio needs to stay on the attack like he has started to do so effectively and portray this Christie endorsement as nothing more than a selfish act,” Desilets said.

In the debate Thursday, Trump said the hiring issue happened decades ago.

Rubio responded: "I guess there's a statute of limitations on lies.”