Janet Napolitano's resignation as secretary of Homeland Security on Friday sets up a potentially bruising fight for President Barack Obama in nominating a successor for the high-profile role.

Napolitano and her department became a point of scrutiny during Obama's first term, as Republicans seized on some of the department's activities, such as the Transportation Security Administration's security practices at airports, DHS's prior knowledge of some attempted terrorist attacks, and the department’s handling and response to the "Fast & Furious" gun-running controversy.

An Andrea Mitchell Reports panel shares their thoughts on reports that Janet Napolitano will step down as Homeland Security Secretary in the fall and become president of the University of California system.

The high-profile position, combined with the ongoing rancor over nominations in the Senate and a broader fight over enforcing border security as part of immigration reform, has all the makings of a contentious battle, regardless of whom Obama picks to replace Napolitano.

Here are some potential candidates for the job:

-- Sen. Susan Collins -- A Republican from Maine, Collins served as chairwoman of the Senate Homeland Security Committee and, later, its ranking Republican member. She is now a member of the Senate Intelligence Committee.

Nominating Collins would offer Obama an opportunity to potentially sidestep a fierce nomination battle by picking a Republican, who would presumably win easy support from her fellow Republican colleagues. Collins is further regarded as a moderate, who has voted with Democrats and the Obama administration on several key initiatives over the past few years.

That said, Collins is up for re-election in 2014. She is seen as having an advantage over Democratic challengers in the race, though her resignation would transform that campaign into a more competitive one if she were to resign.

Perhaps fueling speculation, Collins said Friday that Napolitano had called her to convey the news of her departure.

“We worked together closely on a host of important issues and met regularly to discuss challenges facing the department,” the senator said in a statement.

-- Ray Kelly -- The commissioner of the New York Police Department since 2002, Kelly has been tasked with equipping one of the world's largest police departments to respond to the threat of terrorism.

Kelly originally served as NYPD commissioner during the first bombing against the World Trade Center, and his performance led to speculation that then-President Bill Clinton would name Kelly to lead the FBI. It helps that Kelly is regarded as a tactician who understands the nature of the job already.

Lucas Jackson / Reuters file photo New York Police Department Commissioner Ray Kelly speaks at a news conference in New York, May 16, 2013.

But the commissioner has endured criticism for the wide latitude given to his department in both its anti-terrorism practices and its general law enforcement activities.

It's not clear what kind of reception a high-profile official such as Kelly would get from Senate Republicans. Kelly's predecessor as commissioner -- Bernard Kerik -- was tapped by President George W. Bush to lead the Department of Homeland Security, but his nomination was undone by a variety of revelations about Kerik's personal dealings.

He did find one big ally on Friday from Sen. Charles Schumer, D-N.Y., who called White House Chief of Staff Denis McDonough to push for Kelly.

"The Department of Homeland Security is one of the most important agencies in the federal government," Schumer said in a statement. "Its leader needs to be someone who knows law enforcement, understands anti-terrorism efforts, and is a top-notch administrator, and at the NYPD, Ray Kelly has proven that he excels in all three."

-- Joe Lieberman -- The former Connecticut senator shared control of the Senate Homeland Security Committee for much of the last decade with Collins. A well-established hawk, Lieberman could conceivably win enough bipartisan support to avoid a contentious confirmation fight.

The former Connecticut senator retired in 2012, after spending almost two decades in the Senate, during which time he served as Democrats' vice presidential nominee in 2000.

But Lieberman also alienated some Democrats by doggedly defending some of the national security practices first initiated by President George W. Bush, including the Iraq war. And Lieberman sided with his friend, Arizona Sen. John McCain, over Obama during the presidential election of 2008. Given Obama’s penchant to nominate confidantes to cabinet posts in his second term, it might make a Lieberman pick unlikely.

But Lieberman was an instrumental figure in the creation and rise of the Department of Homeland Security, making it easy to envision his transition into leading the agency.

-- Rand Beers – The current acting deputy secretary of Homeland Security, Beers would enter the secretary’s job with a strong grounding in some of the emergent areas of counterterrorism.

Beers previously headed the department’s National Protection and Programs division, giving him the kind of experience the president might look for in a new homeland security chief. But Beers has also angered Republicans over time, having resigned from President George W. Bush’s National Security Council over concerns preceding the Iraq War. Beers had also been sharply critical in the past of McCain's foreign policy views.

-- Mike Rogers -- The chairman of the House Intelligence Committee, the Michigan Republican's name has been associated with several other high-profile law enforcement vacancies in the Obama administration. Rogers had been tied to potential jobs leading the CIA and FBI, and never fully dismissed speculation for either.

Rogers recently declined running for Senate in Michigan, and has been sharply critical of the administration on the Benghazi controversy and other national security matters. But he could win over skeptical Senate Republicans.

-- Jane Harman -- The head of the Woodrow Wilson International Center for Scholars, Harman distinguished herself during her time in Congress by serving as the ranking member of the House Homeland Security Committee.

Harman was regarded as a moderate Democrat during her time in Congress with broad knowledge of both the national security and foreign policy environments. She had defended some of the Bush administration's surveillance practices, and could have crossover appeal to help her win confirmation.

NBC’s Chuck Todd contributed to this report.

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