The 'amoral bully' is ready to campaign for the 'dishonest politician' as President Donald Trump holds a Houston rally for Sen. Ted Cruz on Monday. The president's appearance on behalf of Cruz represents a once-unthinkable show of support for Trump's onetime rival for the 2016 Republican presidential nomination and comes as Cruz faces a strong challenge from Democratic Rep. Beto O'Rourke. Closing in on Election Day, Trump tweeted Monday morning: 'Big Night In Texas!!!!' In recent weeks, Trump has attacked O'Rourke on Twitter as a 'total lightweight' and a 'flake,' while stressing that Cruz 'has long had my Strong Endorsement.' That's a far cry from Trump's derision of Cruz as 'Lyin' Ted' during the 2016 primaries, when the two traded unusually harsh words for each other. While Trump will promote Cruz and other Texas Republicans, Texas will also provide a backdrop for the president's invigorated immigration rhetoric. Trump escalated that message Monday on Twitter, saying the U.S. would begin 'cutting off, or substantially reducing' aid to three Central American nations over a migrant caravan heading to the U.S. southern border. On recent campaign stops, Trump has raised alarm over thousands of migrants traveling through Mexico, as he tries to make immigration politics part of his closing argument. 'Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws!' Trump tweeted Monday, without mentioning that Republicans have held the majority in the House and the Senate throughout the first two years of his presidency. The president's focus on immigration politics comes as he seeks to counter Democratic enthusiasm in November. But the approach offers both risks and rewards. He could energize Democratic foes as well as the Republicans he wants to rouse to the polls. Trump's Texas stop is part of a campaign blitz that is expected to last until Election Day. Although political relationships tend to be fluid, Trump's appearance for Cruz is notable, given that the two were bitter enemies during the 2016 primaries. After Trump insulted Cruz's wife and father, and Cruz refused to endorse Trump at the Republican convention, it was far from clear that the two would ever put it all behind them. But they started rebuilding in the closing days of the campaign and have worked together since Trump took the White House. 'I think they're neutral,' said former Cruz campaign aide Rick Tyler. 'I think, like a lot of political relationships, they're often transactional.' Trump promised he would come to Texas after the Senate race grew closer than expected, with O'Rourke out-fundraising Cruz and drawing large and enthusiastic crowds around the state. Cruz, who is leading O'Rourke in the polls, said over the summer that he would welcome Trump's support, though he has brushed off any suggestion he'd need Trump to win. During the 2016 Republican primary, Trump assailed Cruz as a liar and 'dishonest politician,' insulted his wife's appearance and promoted unsubstantiated claims that Cruz's father had links to President John F. Kennedy's assassin, Lee Harvey Oswald. Cruz gave back as good as he got. He savaged Trump as a 'pathological liar,' an 'amoral bully' and a 'sniveling coward.' After Cruz lost the primary, he gave a speech at the Republican National Convention in which he did not endorse Trump and instead called on Republicans to 'vote your conscience,' drawing boos from the crowd. But he announced his support about a month before Election Day — and won points in Trump's camp for not withdrawing after the 'Access Hollywood' tape was released in which Trump bragged about groping women. 'That was a real concern because he had just endorsed two weeks earlier,' said former Trump campaign aide Andy Surabian. 'I think that's the moment when the detente started and the moment when Ted and the president's relationship began to shift for the better.' Since Trump took office, Cruz and his wife have dined at the White House, and Cruz has said his office is in regular touch with the White House on policy. Still, in an interview aired over the weekend on ABC, he dodged a question on whether the two were friends or foes. 'He's the president,' Cruz said. 'I work with the president in delivering on our promises.