Trump will travel to Texas to hold a massive get-out-the-vote rally for Cruz in the final days of a closer-than-expected race against Rep. Beto O'Rourke (D).

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For Cruz, the rally is born of necessity -- polling shows him with a mid-to-upper single digit lead over O'Rourke, but the incumbent badly needs an energized Republican base in order to ensure victory. And no one rallies the Republican base like President Trump.

For Trump, it's the latest example of a former political foe -- and one who he attacked (and was attacked by) fiercely -- seeking to make peace, with an acknowledgment that, well, standing against him just wasn't worth it.

From Sens. Rand Paul to Lindsey Graham to Cruz, Trump has watched as his fiercest critics have turned into, at least in the case of Paul and Graham, two of his staunchest allies. That willingness to seek political peace speaks to Trump's total and complete takeover of the Republican Party over the past three years. There is simply no safe political space for Republicans on the wrong side of Trump. Retiring Arizona Sen. Jeff Flake (R) is retiring because he wrote a book questioning Trump's grip on the GOP. Retiring Tennessee Sen. Bob Corker (R) is retiring, at least in part, because he took a hit when he stepped out and criticized some of Trump's controversial comments.

Which brings us back to Cruz. And Trump.

Somewhat amazingly, the 2016 Republican primary fight left these men as the last two standing -- albeit with a clear edge for Trump, who had opened a significant delegate lead thanks to a series of early wins. (Prior to the race narrowing, Cruz had repeatedly -- and publicly -- refused to attack Trump, insisting that was only doing what the media wanted.)

As winter turned to spring, however, Trump took direct aim at Cruz -- labeling him "Lyin' Ted." Over and over again, Trump said some version of this: "Lyin' Ted. Lies. Ooh, he lies. You know Ted. He brings the Bible, holds it high, puts it down, lies." From March 13 to May 6 -- the heart of their heated battle, Trump tweeted the phrase a whopping 27 times, according to the Dallas Morning News

Asked about his history of insults on Monday before the rally, Trump told reporters: "He's not Lyin' Ted anymore. He's Beautiful Ted. I call him Texas Ted."

It wasn't just the name-calling, though. Trump also attacked the fact that Cruz was born in Canada, suggesting that the Texas senator, whose mother was a US citizen, was not sufficiently loyal to the country.

"Why would Texans vote for 'liar' Ted Cruz when he was born in Canada, lived there for 4 years-and remained a Canadian citizen until recently," Trump asked in a tweet in February 2016. Trump also obliquely suggested that Cruz's father, Rafael, might have been involved in the assassination of former President John F. Kennedy because a picture existed showing someone resembling the elder Cruz and Lee Harvey Oswald together. (The Cruz campaign denied that it was Rafael Cruz in the picture.)

The breaking point between Trump and Cruz wasn't any of that, however. (And, yes, that is amazing.) It was when Trump tweeted an unflattering picture of Heidi Cruz, the senator's wife, next to a picture of his own wife Melania; "The images are worth 1,000 words," read text on the picture

Cruz went bananas. In an angry press conference, he said Trump had gone too far.

"I don't get angry often," said Cruz. "But you mess with my wife, you mess with my kids, that will do it every time. Donald Trump, you're a sniveling coward. Leave Heidi the hell alone."

Eventually, the math caught up with Cruz. He bowed out. But he didn't endorse Trump. Despite that lack of full support, Cruz was given a primetime speaking slot at the 2016 Republican National Convention in Cleveland; the Trump forces believed Cruz was ready to publicly throw his full backing behind the nominee.

NOPE!

"We deserve leaders who stand for principle," Cruz said at the close of his speech . "Unite us all behind shared values. Cast aside anger for love. Every one of us has an obligation to follow our conscience." The next morning, Cruz was defiant. "I am not in the habit of supporting people who attack my wife and attack my father," he said.

Trump was reportedly livid but tried to play off Cruz's snub as NBD. "Wow, Ted Cruz got booed off the stage, didn't honor the pledge!," tweeted Trump . "I saw his speech two hours early but let him speak anyway. No big deal!"Despite insisting he didn't want and wouldn't accept Cruz's endorsement following the convention snub, Trump did just that in late September 2016. "A year ago, I pledged to endorse the Republican nominee, and I am honoring that commitment," Cruz wrote in a Facebook post . "And if you don't want to see a Hillary Clinton presidency, I encourage you to vote for him."

Fast forward to now. Cruz has avoided any direct criticism of Trump since the election, a) knowing the danger that presents to any Republican and b) being mindful of his need to win a second term.

In late August, all of Cruz's playing nice with Trump paid off.

"I will be doing a major rally for Senator Ted Cruz in October," Trump tweeted . "I'm picking the biggest stadium in Texas we can find. As you know, Ted has my complete and total Endorsement. His opponent is a disaster for Texas - weak on Second Amendment, Crime, Borders, Military, and Vets!"

That "major rally" is tonight. But even on the eve of what is expected to be a massive event in Houston, Cruz still seemed somewhat sparse in his praise of Trump in a story that aired on "This Week with George Stephanopoulos" on Sunday

"He's the President," said Cruz. "I work with the President in delivering on our promises. What I told the President the week after the election, I said, 'Mr. President, I want to do everything humanly possible to roll up my sleeves and lead the fight in the Senate to deliver on our promises."

While Cruz may not love having to need Trump, he knows it's his best chance at surviving in 15 days. And Cruz is far from the first former foe to bow down to the President's political power.

Like Cruz, it's hard to separate out the conversion experiences of Paul and Graham from political concerns. All three men have taken on water, politically, with their attacks on Trump. Getting right with Trump was the only option unless they wanted to face the prospect of losing their seats the next time they ran for reelection.

That reality is Trump's ultimate revenge on all his former foes. This is HIS party now. They either need to recognize it and kiss the ring or run the risk of not having a job. And so, because they are politicians, they kiss the ring. (Or at least most of them do.)

So, when he takes the stage in Houston on Monday night, Trump is doing so ostensibly to support Cruz. But Trump is also asserting his total control over Cruz -- and that's the part Trump likely enjoys more.