Republican Sens. Jeff Flake of Arizona and Bob Corker of Tennessee, who made headlines this week for their eviscerating denunciations of President Trump, may be retiring from Congress – but their exits won’t actually come for another 14 months, an eternity in politics. Which raises the question: How might these lawmakers translate their stated opposition to the president into concrete actions over the course of the next year?

Both men, along with Arizona Sen. John McCain – another GOP heavyweight and prominent Trump critic – have made it plain that they intend to act on their concerns in the time they have left in the Senate. Senators Corker and McCain are chairmen of two powerful committees, Foreign Relations and Armed Services, and as such are in a strong position of oversight – able to call hearings that can make a president’s life miserable (think “Benghazi”), issue subpoenas, and stall nominees.

McCain, who has been diagnosed with cancer, has particular power because he shepherds must-pass military spending legislation, the National Defense Authorization Act, which is nearing completion.

It would be a mistake to think of these three as a cabal, attempting to corral their colleagues or planning to kneecap the president at every opportunity. Corker told reporters he’s not trying to “herd” others. Senator Flake says he has no “vindictive” plan to block Mr. Trump’s agenda – an idea that’s just “dumb,” agrees McCain. They say they will work with the president on areas where they agree.

But on the areas where they think the president is wrong ­– or endangering the nation, as all three have suggested – they can command a bright spotlight and act as a tangible check on his power.

“Those chairmen are in a feisty mood toward the White House. They may not choose to do much, but they can do a lot,” says Christopher Kojm, a former Hill committee staffer and now professor at the Elliott School of International Affairs at George Washington University in Washington.

In practical terms, it may be similar to having the opposition party in control of parts of Congress, at least to some degree. And history has shown that when the opposition comes from the president's own party, it can be particularly powerful. The hearings that Democratic Sen. J. William Fulbright, another Foreign Relations chair, held on the Vietnam War, for example, were seen as instrumental in turning opinion against the war – and against President Lyndon Johnson.

McCain has been flexing his chairmanship muscles already, threatening subpoenas and holding up Pentagon nominees to pry more information about military strategy and activity from the administration. He said Thursday he would lift some of those holds because the administration finally briefed members this week on four US troops who were killed in an ambush in Niger.

Likewise, Corker is planning a schedule of vigorous hearings on everything from the authorization to use military force, to the Iran nuclear deal, to international agreements that the president is bashing but which Corker sees as beneficial to the United States. He names trade as one of those areas.

“The committee’s going to be very active,” Corker told reporters on Wednesday. “It’s going to be a very robust period of time beginning Monday night at 5 o’clock.”

Authorization for Use of Military Force

That’s when Foreign Relations committee members – including Flake – will question Secretary of State Rex Tillerson and Secretary of Defense Jim Mattis at a hearing about war powers and congressional authorization to use military force. It’s a subject of renewed interest given the administration’s investigation into what happened in Niger, the growth of ISIS and its affiliates in Africa, and grave concerns about North Korea.

The hearing holds the potential for sparks, despite the fact that Corker is strongly supportive of both Mr. Tillerson and Mr. Mattis. He has made clear he views them as guardrails against a president whose stability and competence he questions.

The immediate subject of the hearing is whether Congress should pass a new Authorization for Use of Military Force (AUMF) to fight terrorism, given that the last two such authorizations date back to 2001 and 2002, on the heels of the 9/11 attacks.

The Trump administration believes they are still valid, as did President Obama, and they are still being used as legal justification for military operations around the globe. Some members of Congress side with the administration, but others say that, as the fight against terrorism has evolved over the past fifteen years, it’s time for Congress to take back its constitutional authority and publicly debate and revise the authorizations.

North Korea is also sure to come up at Monday’s hearing, as members in both parties worry the president may be boxing the US into a military confrontation while prematurely closing the door on diplomacy. Related are questions of war powers, since the Constitution gives Congress the power to declare war, while the president is commander in chief.

“I hear widespread concern about the president short-circuiting diplomatic efforts between the United States and North Korea, and having no clear plan for an off-ramp,” says Sen. Chris Coons (D) of Delaware who is a member of Corker’s committee. “If the president wants a military confrontation with North Korea, he is capable of moving us into a position where that becomes unavoidable unless Congress acts.”

Democrats like Senator Coons share Corker’s concerns about Trump, and Corker can expect to find backing from them, as well as from some Republicans like Flake – who is working with fellow committee member Tim Kaine (D) of Virginia on a new AUMF authorization.

The devil's in the details

But agreeing on the details of an AUMF, which would need to take shape as legislation, will be easier said than done. And other Republicans may not want to appear as crossing their president.

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“Once you move into the realm of legislation, then you start to come up against the problem of the rest of your party and to what extent do other Republicans want to challenge their president,” says Paul Saunders, a former State Department advisor, speaking generally about Trump critics trying to move bills that the president opposes. Mr. Saunders, who is the executive director of the Center for the National Interest, notes that other Republican senators aren’t publicly embracing the warnings that Corker, Flake, and McCain are sounding about Trump.

Indeed, most GOP lawmakers have been largely dismissive, framing the criticism as “simply some personality clashes,” as Sen. James Risch (R) of Idaho put it in an interview. Senator Risch has been mentioned as Corker’s possible successor as Foreign Relations chair when Corker retires.