Houston (CNN) President Donald Trump declared himself a "nationalist" during his rally here on Monday night, officially tagging himself with the label that has long defined his populist rhetoric and protectionist policies.

"A globalist is a person that wants the globe to do well, frankly not caring about the country so much. You know, we can't have that," Trump said, prompting boos from the crowd.

"You know what I am, I'm a nationalist," he added, as the crowd erupted in "USA! USA!" chants. "Use that word."

The comment marked the first time Trump has directly associated himself with the political ideology, which has long defined his outlook and the protectionist trade policies he has implemented in an effort to boost domestic manufacturing.

The remark came during a nearly hour-and-a-half-long rally in the arena that is home to the Houston Rockets, where the President rallied his base in this deeply red state 15 days before the midterms, stoking fears about illegal immigration, painting Democrats as criminal accomplices and basking in the glory of his accomplishments.

With his visit ostensibly aimed at boosting Sen. Ted Cruz's re-election bid, the President took the stage after an introduction from his former political nemesis by addressing the elephant in the room.

"You know, we had our little difficulties," Trump said to laughter from the nearly full house at the 18,000-capacity Toyota Center in downtown Houston.

He and Cruz, Trump said, had begun the 2016 presidential campaign as allies, rallying conservatives together in Washington early in the campaign. But eventually, Trump said, the two men decided it was "time" to begin hitting each other.

"And it got nasty," Trump said.

But since he was elected, Trump said, Cruz has been one of his top allies in Congress.

"And then it ended and I'll tell you what, nobody has helped me more with your tax cuts, with your regulation, with all of the things ... including military and our vets, than Sen. Ted Cruz," Trump said as he predicted that "in just 15 days the people of Texas are going to re-elect a man who has become a really good friend of mine."

It was a stark change from the spring of 2016, when Trump was whipping that same base of support into a frenzy against "Lyin' Ted."

Earlier Monday the President had given the senator from Texas a pair of much kinder monikers.

"To me, he's not Lyin' Ted anymore. He's Beautiful Ted. He's Texas -- I call him Texas Ted," Trump said as he left the White House en route to Houston.

"No, Ted Cruz and I had a very, very nasty and tough campaign. It was a very competitive -- it was a very tough campaign. Once it ended and we got together -- and, by the way, very late into the campaign we lasted. People were shocked. I said, 'Don't worry, it's only a question of time,' " Trump said.

To the dismay of some Republicans in tighter races, Trump was stumping in Texas to help ensure Cruz fends off a challenge from Democratic Rep. Beto O'Rourke, whose energized campaign has unnerved some Republicans.

Trump's Texas rally is just the latest stop in the President's blitz of campaign appearances leading up to the midterm elections November 6, coming on the heels of a swing through Western states late last week.

And the President largely stuck to the closing argument he has developed over the last week to galvanize his supporters into supporting down-ballot Republicans, with illegal immigration at the heart of his message.

With a caravan of several thousand migrants making its way from Central America toward the US border, the President has upped his rhetoric, warning voters -- without evidence -- about criminal elements embedded in the caravan and saying earlier on Monday (also without evidence) that "Middle Eastern" people were among them.

Delivering his latest screed against Democrats and the immigration policies for which he holds them responsible, Trump repeatedly tied the Democrats to crimes committed by undocumented immigrants.

"The Democrats have launched an assault on the sovereignty of our country, the security of our nation and the safety of every American," Trump said, blaming them entirely for "the crisis on our border."

After falsely accusing Democrats of wanting to "give aliens free welfare and the right to vote" and of wanting "open borders," the President stressed the importance of expanding Republican majorities in Congress in order to change immigration laws.

"We don't have enough votes. As an example, with the Senate we need 60 votes. We have 51. We need 60 votes. So they don't allow us to do it. They're killing and hurting innocent Americans," Trump said, before diving back into MS-13 crimes, accusing "Democrat immigration policies" of allowing members of the gang and drugs to illegally enter the US.

At one point, Trump graphically detailed MS-13's brutality, saying the gang preferred to use knives instead of guns.

"They like cutting people up, slicing them," the President said. "Killing them, slicing them."

Trump next will rally supporters in Wisconsin and North Carolina and then round out the week in Illinois.

Monday's rally came as he continues to grapple with one of the most consequential diplomatic crises of his presidency, the fallout from the death of Saudi journalist Jamal Khashoggi, who was killed by Saudi agents in the Saudi Consulate in Istanbul earlier this month.

Saudi Arabia admitted for the first time on Friday that Saudi officials had killed Khashoggi, but claimed it was an accidental death resulting from a fistfight -- an explanation at odds with the Turkish government's account and other key facts.

Trump has turned away from that issue during rallies, however, instead focusing on his accomplishments as President and warning his supporters that Democratic gains in Congress would spell disaster for the country.

He did not address the Khashoggi issue during his rally on Monday night.