WASHINGTON (Reuters) - Several names surfaced on Monday as possible successors to U.S. Homeland Security Secretary Kirstjen Nielsen, who resigned on Sunday after 16 months managing President Donald Trump’s turbulent immigration agenda.

Homeland Security Secretary Kirstjen Nielsen speaks during a border security briefing held for U.S. President Donald Trump near the US-Mexico border in El Centro, California, U.S., April 5, 2019. Picture taken April 5, 2019. REUTERS/Kevin Lamarque

Amid a surge in the number of migrants at the border with Mexico, Nielsen stepped down and will be replaced temporarily by Kevin McAleenan, current head of U.S. Customs and Border Protection.

As Trump seeks a permanent nominee to send to the Republican-controlled Senate for confirmation, here are some possible successors whose names have already been floated by sources talking to Reuters and in media reports. None immediately responded to requests for comment.

RICK PERRY

Trump’s energy secretary has kept a relatively low profile since winning confirmation by a vote of 62 to 37.

As Texas governor from 2000 to 2015, Perry was on the front lines during a spike in migrants seeking asylum in 2014. He opposed building a wall along the U.S.-Mexico border at the time, but now supports Trump’s signature domestic policy.

KEN CUCCINELLI

The former Virginia attorney general visited the White House last week amid reports that Trump was searching for an “immigration czar” to coordinate policy across the government.

As attorney general and state senator, Cuccinelli developed a reputation as a conservative hard-liner on a range of issues, including immigration. He has called for denying citizenship to U.S.-born children whose parents are in the country illegally, and authorized law enforcement officials to investigate the immigration status of anyone they stopped.

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He lost a bid for governor in 2013, and recently has been involved with the Senate Conservatives Fund, a political group that supports right-leaning candidates.

KRIS KOBACH

The former Kansas secretary of state has built a national reputation as an uncompromising opponent of illegal immigration.

Since losing the Kansas governor’s race last November, Kobach has been angling for a job in the Trump administration, telling Breitbart News over the weekend that he would be open to serving as a White House immigration “czar.” He also proposed blocking illegal immigrants from sending money back to Mexico.

Kobach could have a hard time winning Senate confirmation due to his hard-line views and unsuccessful 2018 campaign, where he lost to a Democrat in a heavily Republican state.

FRAN TOWNSEND

A former homeland security advisor to President George W. Bush, Townsend now is an analyst for CBS television. She says Trump considered her as a possible replacement for FBI Director James Comey after he was fired in 2017.

KEVIN MCALEENAN

As commissioner of U.S. Customs and Border Protection, McAleenan said last month that the immigration system was at a “breaking point.” A career law enforcement official, McAleenan has served on and off in the division since its inception after the Sept. 11, 2001 attacks.

McAleenan has won the respect of Republicans and Democrats and easily won confirmation to his current post in March 2018 by a vote of 77 to 19.

He has pushed Congress to detain families seeking asylum until their cases are heard in court, rather than releasing them. However, he has not always lined up with Trump’s aggressive approach to border security. He has praised the effectiveness of U.S. aid to Central America, which Trump has threatened to cut off.