With the midterm elections days away, however, the Cruz-Trump relationship looks remarkably different.
Trump also took aim at Cruz's opponent, Robert "Beto" O'Rourke, calling him far too liberal for Texas.
"I'll tell you what: Nobody has helped me more, with your tax cuts, with your regulation, with all of the things that we're doing, including military and our vets, than Senator Ted Cruz", Trump told the 18,000 assembled faithful.
The president acknowledged that his primary campaign against Mr. Cruz in 2016 was "nasty".
"In 2020, Donald Trump will be overwhelmingly reelected as president of the United States", Cruz said, prompting a chorus of cheers from the crowd.
Despite O'Rourke's national buzz as a progressive liberal over-performing in the conservative bastion of Texas, he still trails in most polls by almost ten points.
"To protect your state and your country, you need to elect a Republican House and a Republican Senate", Trump said.
The president took to the stage alongside senator Ted Cruz Monday, where the two touted the success of republican policies and how they've benefited the American people. "Donald Trump won OH by 8.1 percent, he won Texas by 9 percent - people think of OH as a purple state, they don't think of Texas as one".
Senator Ted Cruz has been locked in a close battle against his Democrat challenger, Congressman Beto O'Rourke of El Paso, who has outraised him about three to one, and who's within single digits.
Inside the arena, the crowd was raucous and loud, waving campaign signs and cheering loudly for Trump and the Republican speakers who preceded him. "I think he's a highly overrated guy".
In May 2016, the President told Fox news: "Cruz's father was with Lee Harvey Oswald prior to Oswald's being - you know, shot".
Chilling... Trump blowing the White Nationalist dog whistle at a rally for #TedCruz. The last time the Democratic party won a statewide race was 1994; Cruz's seat should be safe.
"I think the Democrats had something to do with it". (Horse-race midterms types would point out here that this makes little strategic sense, as Cruz is projected to win tidily and the president's time might be better spent throwing a bone to less safe GOP candidates.) But Cruz seemed nearly an afterthought throughout.
He said: "He's not lyin' Ted anymore".