URBANDALE, Iowa — From D.C. to Des Moines, Marco Rubio supporters believe he is the least like Donald Trump of all the top-tier Republican presidential candidates.

They see him as optimistic rather than voicing gloom and doom, cheerful and positive rather than dark and negative, welcoming rather than fearful and capable of expanding conservatism's appeal beyond angry white men. Those are some of the things the 1,000 or so people who turned out to see Rubio at the Ramada Tropics Resort and Conference Center on Saturday night like him about him.

"Anger is not a plan," Rubio said in one of his few thinly veiled jabs at Trump.

But in subtle ways, even Rubio has to adapt his message to Trump and the climate of anger that has made the billionaire the prohibitive front-runner in Iowa and beyond. The first and most obvious is on immigration.

It's not news that Rubio has jettisoned his support for the 2013 Gang of Eight bill, a bipartisan initiative that would have created a path to citizenship for illegal immigrants and vastly increased legal immigration. He no longer merely says that he learned that Republicans and other voters aren't ready for comprehensive reform or won't trust it until the border is secure, however.

"The world has changed," Rubio said. "The biggest priority is now keeping ISIS out of the United States." He has said similar things in recent Republican debates. When he used this line in Urbandale, the crowd let out scattered cries of, "Yes!"

While Rubio began with a preamble about his own experience as a son and neighbor of immigrants, he told his audience that if you were going to come to America "we need to know who you are and what you're doing here."

Rubio promised to complete the border security fence, implement an entry-exit tracking system to crack down on visa overstayers, hire 20,000 new border patrol agents instead of new IRS agents and, most important of all, not even entertain more comprehensive reforms — that is, amnesty — until the immigration process is secure.

Whether you believe Rubio or not, he sounds much more like the immigration hawk who was elected to the U.S. Senate from Florida in 2010 than the Gang of Eight member he became three years later. His precise argument not only gives him a stronger rationale for his shift than simply addressing a political liability with conservatives, it better fits an electorate that views terrorism as an immigration and border security issue as much or more than a foreign policy issue.

Rubio is an upbeat and confident American exceptionalist. But his view of Barack Obama's America can sound as dark as any other Republican presidential candidate's.

"Everything that made America great is now in question," he said. We have a president "who completely ignored the Constitution as a matter of course," who "wanted to change America," who saw the United States as an "arrogant global power," a "nation that needed to be cut down to size," who likes to "apologize for America."

Sen. Charles Grassley, R-Iowa, said in his introduction that Obama wanted to "transform America" while Rubio wanted to "preserve America."

In a more rhetorically restrained fashion, Rubio even gave us a little bit on China and other foreign nations humiliating our leaders on the world stage and beating them in negotiations. He talked about Chinese government hackers, Iran sanctions relief that will be used to "beef up their military" and eventually build a nuclear bomb, and a military that has been gutted and hollowed out.

"I will never seek to pit Americans against each other," Rubio said. But he was contrasting himself with Obama, not Trump. "I will never seek to win an election by pitting Americans against each other the way our current president has," he said earlier.

Toward the end of his speech, Rubio even said that one of the two options for voters in the 2016 presidential election is to ensure "America becomes greater than she ever was." Rubio was calling for a return to the republic's founding principles, but it was the second time in one speech he said something that bore a passing resemblance to "Make America great again."

Context matters. There are rhetorical and substantive distinctions to be made between Rubio and Trump. Even one of the past happy warriors of the American right, Ronald Reagan, could sound apocalyptic at times, especially in the 1960s. A successful politician must tap into the electorate's mood and try to compete with what has worked for rivals. Trump's message has been working for him so far.

But it's a testament to Trump's impact on the GOP race that even the candidate whose supporters love his anti-Trump persona cannot completely ignore him.