The controversial sheriff of Arizona's Maricopa County, Joe Arpaio, announced his endorsement of Republican presidential contender Donald Trump saying that it was a "no brainer." (Reuters)

MARSHALLTOWN, Iowa -- Joe Arpaio, the prominent and controversial sheriff of Arizona's Maricopa County endorsed Republican presidential candidate Donald Trump on Tuesday, uniting a law enforcement official known for his unyielding efforts to stop and expose undocumented immigrants with a candidate who has made border security a central theme of his candidacy.

Arpaio flew to this tiny town on Tuesday to endorse Trump in person, calling him a "great patriot" and someone "easy to endorse."

"Everything I believe in he’s doing and he’s going to do it when he becomes president," Arpaio told reporters shortly after addressing hundreds of Trump supporters waiting in a high school gymnasium here. "I met Donald six months ago in Phoenix, introduced him then, 30 days back in Phoenix, introduced him then. It is my privilege and honor to help him, to endorse him today for president of the United States."

The brash sheriff is perhaps best known for his close association to the controversial 2010 Arizona law that directed local authorities to routinely stop people they suspected of being undocumented immigrants, for the purpose of determining their legal status. Arpaio has been repeatedly accused of racial profiling and discrimination against the area's Hispanic residents.

Arpaio's endorsement of Trump will likely be applauded by anti-immigration activists who say Arpaio’s uncompromising efforts are necessary because of the federal government’s inaction on the issue. But Trump’s liberal critics have already lambasted the endorsement, which they say is yet another display of Trump’s hard-line anti-immigrant rhetoric.

"Today Donald Trump continued his efforts to divide Americans on his way to the GOP nomination by accepting the endorsement of infamous anti-immigrant Sheriff Joe Arpaio in Marshalltown, a city with one of the largest Latino populations in Iowa," said Pablo Manriquez, the Hispanic media director at the Democratic National Committee.

The so-called “show me your papers” law, at the time dubbed the toughest immigration law in the country, notably triggered a high-profile legal challenge from the Obama administration. Although the Supreme Court struck down several aspects of the law — including one provision that would make it a misdemeanor for immigrants to not carry registration documents — it nonetheless upheld the provision requiring officers to check the immigration status of those they stopped.

Arpaio addressed the crowd before introducing Trump at a press conference, so most reporters didn't see the sheriff in front of the crowd. Trump was clearly pleased with the endorsement.

"This is a man when we talk about borders, this is a man that believes in borders and getting his endorsement means a lot to me," he said.

On Tuesday Trump also announced the endorsement of Liberty University president Jerry Falwell Jr., the son of late televangelist.

DelReal reported from Washington.

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[Supreme Court upholds key part of Arizona law for now, strikes down other provisions.]

[Sheriff Joe Arpaio’s day in an Arizona court.]