FILE - In this Nov. 14, 2018, file photo, from left, Sen. Mike Lee, R-Utah, former Virginia Attorney General Ken Cuccinelli, and Sen. Chuck Grassley, R-Iowa, laugh before President Donald Trump arrived to announce his support for the first major rewrite of the nation's criminal justice sentencing laws at White House in Washington. Cuccinelli has been named acting director of U.S. Citizenship and Immigration Services. (AP Photo/Andrew Harnik, File)

WASHINGTON (AP) — An outspoken supporter of President Donald Trump's hardline immigration policies has been named acting director of the agency that manages legal immigration, despite deep opposition from key Senate Republicans.

Ken Cuccinelli will oversee U.S. Citizenship and Immigration Services starting Monday, Department of Homeland Security Acting Secretary Kevin McAleenan announced.

But it's unclear if Trump will nominate Cuccinelli for the permanent position. That would require Senate confirmation, which could be difficult. Instead, Trump may simply opt to keep Cuccinelli in the acting position, a work-around to rules governing vacancies that sparked Senate objections.

"I don't think that's a wise move," said Sen. Marco Rubio, R-Fla., who warned bypassing the confirmation process could spill over into other nominations.

The second-ranking Republican, Sen. John Thune of South Dakota, said the preference would be for Trump to submit the nomination, "and go through the process and have a confirmation hearing and an opportunity for a vote."

Said Thune: "We think that's the way really if you want to solidify people in these positions. But they've chosen a different path."

Cuccinelli is a former Virginia attorney general who ran for governor of Virginia, but lost to Democrat Terry McAuliffe in 2013. He has in the past advocated for denying citizenship to the American-born children of parents living in the U.S. illegally.

It's not just Cuccinelli's views on immigration that would generate unease among senators. As the former head of the Senate Conservatives Fund, Cuccinelli has been highly critical of Senate GOP leadership, including once advocating for the removal of Senate Majority Leader Mitch McConnell and his entire leadership team.

The group backed conservative candidates for Senate and primary challengers for incumbent Republicans, putting it at odds with the party's chosen candidates. His group and others complained McConnell was insufficiently delivering on conservative priorities, including immigration.

And he helped lead the failed 2016 effort by Trump's chief rival, Sen. Ted Cruz, to secure a rules vote that would have complicated Trump's nomination as GOP candidate for president.

One Republican familiar with the situation said the White House has been made aware that Cuccinelli would have a difficult time winning confirmation in the Senate, where Republicans have the majority. The person, granted anonymity to discuss private conversations, said confirmation would be a tough lift.

Facing a potential confirmation battle, it appears the Trump administration placed Cuccinelli in a new position that could be a way to work around federal regulations that limit how long people can serve without Senate confirmation, one legal expert said.

Democrats signaled strong opposition.

Rep. Bennie Thompson, D-Miss., the chairman of the House Homeland Security Committee, called Cuccinelli "an anti-immigrant fringe figure that has no business" helming a key component of the nation's immigration system.

"Besides being a right-wing commentator, Cuccinelli is completely unqualified to the lead USCIS," he said in a statement. "With both Democrats and Republicans opposing him, there is no reason for President Trump to instill someone who has no chance of Senate confirmation."

Citizenship and Immigration Services is the agency responsible for legal immigration, including benefits and visas. The position opened after Trump forced the resignation of Lee Francis Cissna , who Trump believed wasn't doing enough. Cissna said he worked "passionately."

The departure last month came amid a White House-orchestrated shakeup at Homeland Security, including the April resignation of Secretary Kirstjen Nielsen.

There are more than a dozen vacancies of top leadership positions at the sprawling, 240,000-employee department. This comes as the Trump administration is struggling with a migrant surge at the southern border that is straining federal resources.

Cuccinelli's name has been mentioned for months to become part of the administration, including as possible Homeland Security secretary or as an immigration czar . There was debate within the Trump administration over whether that czar's position would be housed within the White House or within Homeland Security, a trickier spot where the appointment could conflict with top leaders in Senate-confirmed positions.

"Our nation has the most generous legal immigration system in the world and we must zealously safeguard its promise for those who lawfully come here," he said in a statement Monday.

The action comes as the department is calling on Congress to provide $4.5 billion more in aid for the border crisis and Trump eased off his threat to impose tariffs on Mexico unless it helps stem the number of Central American migrants flowing over the border. Mexico agreed to greatly ramp up sending asylum seekers back over the border to wait out their cases and will send National Guard troops to its southern border.

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Associated Press writer Alan Fram in Washington contributed to this report.