Updated 9:15 a.m.
With Congress poised to spend the next several days debating the merits of U.S. military action in Syria, the Obama administration is deploying top national security officials to Capitol Hill this week to testify in public and brief lawmakers behind closed doors.
But the White House is also relying on several influential members of the House and Senate to rally support, while the opinions of certain rank-and-file members could attract special attention.
Based on our reporting, here's a look at 12 key individuals or groups of lawmakers to watch in the coming days:
Senate Majority Leader Harry M. Reid (D-Nev.): The White House will be leaning on the Senate leader to help rally sufficient support for a use of force resolution, especially if senators threaten to filibuster the measure. Several Democratic senators already have said they oppose or are skeptical of the use of military force in Syria, potentially complicating his efforts. Reid voted to authorize military action in Iraq, but later emerged as a leading critic of the war.
Senate Minority Leader Mitch McConnell (R-Ky.): Will he work as Senate Republican leader to rally support, or allow colleagues to vote their conscience? McConnell said Tuesday that he appreciated meeting with Obama, but that "Congress and our constituents would all benefit from knowing more about what it is he thinks needs to be done -- and can be accomplished -- in Syria and the region." Facing reelection next year, McConnell is struggling to hold together the Senate GOP conference and on several issues has faced resistance from tea party-backed senators unwilling to be seen supporting administration policies. McConnell also has faced tension from moderate Republicans more eager to strike bipartisan deals with the White House.
House Republican leadership: Speaker John A. Boehner (R-Ohio), Majority Leader Eric I. Cantor (R-Va.) and Majority Whip Kevin McCarthy (R-Calif.) issued a joint statement this weekend calling on Obama to provide Congress with more information and welcoming the forthcoming debate. Boehner and Cantor said they would vote for a strike after meeting with Obama on Tuesday, while McCarthy hasn't signaled how he would vote. The trio has struggled to hold together the House GOP Conference on key votes this year and has been forced to quickly withdraw some legislation that faced defeat. They are not expected to formally count votes on any resolution, and aides say that Democrats will also need to rally sufficient support.
House Minority Leader Nancy Pelosi (D-Calif.): She is strongly backing military action in Syria, putting her at odds with dozens of liberal colleagues, primarily from urban districts, who are either opposed to military action or still weighing how to vote. Pelosi is a known vote-getter who can wield her influence on wavering colleagues when needed. Pelosi voted against the use of force in Iraq in 2002.
Committee chairmen: The White House is paying special attention to the chairmen and ranking members of the House and Senate foreign relations, armed services and intelligence panels, hoping that united support from them will bring along undecided lawmakers. Pay special attention to House Intelligence Committee Chairman Mike Rogers (R-Mich.), who narrowly succeeded in defeating a House resolution to defund some National Security Agency programs. House Armed Services Committee Chairman Howard "Buck" McKeon (R-Calif.) and House Foreign Affairs Committee Chairman Ed Royce (R-Calif.) could help lobby members of their committees, plus the 11 other California Republicans in the House. Rep. Eliot Engel (D-N.Y.), ranking member on the Foreign Affairs Committee, has been in close touch with administration officials and might also be able to rally colleagues from New York and other states who have signaled opposition to a resolution.
Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.): The pair wield great influence over GOP colleagues on foreign policy debates, partly due to their outsized influence on the nation's airwaves. Taking advantage of their long-term negotiating posture with the administration, they scored a White House meeting Monday with the president and emerged to announce their support for a military resolution. McCain is a reluctant supporter: "I don’t think the president should have done this," he told "CBS This Morning" on Tuesday. "Once he announced that we were going to have strikes, I think he should have acted, as other presidents have, both Republican or Democrat. But it is what it is." Graham is generally supportive, but believes Obama needs to do more to convince skeptical lawmakers, aides said.
Republicans thinking about 2016: There are at least four GOP lawmakers weighing serious bids for the White House, or who could end up on the short list of vice presidential contenders. In the Senate, keep an eye on Sens. Ted Cruz (R-Tex.), Rand Paul (R-Ky.) and Marco Rubio (R-Fla.), who have all expressed skepticism. Ditto Rep. Paul Ryan (R-Wis.), who waited until Tuesday morning to signal that he's still unconvinced.
Democrats thinking about 2016: Depending on what Hillary Rodham Clinton and Vice President Biden decide to do, there are a handful of Democratic lawmakers waiting in the wings to run for president. In the Senate, keep an eye on Sens. Kirsten Gillibrand (D-N.Y.) and Amy Klobuchar (D-Minn.), who have both hinted at broader national ambitions. Some Democrats also have talked about Rep. Joaquin Castro (D-Tex.) (or his brother, San Antonio Mayor Julian Castro) as a possible dark horse vice presidential candidate in three years.
Rep. Justin Amash (R-Mich.): One of the most vocal and renegade House Republicans, the Michigan lawmaker has been actively voicing his opposition to military action on Twitter. On Sunday he showed up for a closed-door Capitol Hill classified briefing on Syria wearing a Darth Vader T-shirt. He joined with liberal Democrats recently to sponsor a resolution to defund several NSA eavesdropping programs that only narrowly lost in the House.
Rep. Scott Rigell (R-Va.): He convinced more than 140 colleagues to sign a letter asking Obama to seek formal authorization for military action and has since said he remains opposed to military action. Rigell represents a Virginia district that is home to hundreds of thousands of active and retired military service members, and he, like many other lawmakers, is sensitive to how wars in Iraq and Afghanistan have strained military families.
Rep. Barbara Lee (D-Calif.): A leading anti-war liberal, she convinced more than 60 colleagues to sign a similar letter to Obama and remains opposed to military action. Given her vocal stance, she could be especially influential over colleagues in the Congressional Black Caucus, a bloc of more than 40 votes that the White House will need to ensure passage of a resolution in the closely-divided House.
Undecided Senate Democrats: There are several senators who caucus with Democrats who say they are skeptical of military action and will need to be convinced to support a resolution, especially if Reid needs a supermajority of 60 senators to ward off a threatened filibuster. This group includes Sens. Joe Manchin III (W. Va.) and Angus King (I-Maine), who could be a key independent swing vote in either direction.
Follow Ed O'Keefe on Twitter: @edatpost
UPDATE 6:56 p.m.: This post has been updated to add McConnell's statement Tuesday about the debate, to clarify Graham's position and to remove Sens. Tom Udall (D-N.M.) and Tim Kaine (D-Va.) from the group of undecided senators.