When it convenes Tuesday, the Republican-controlled 114th Congress will bring a wave of reinforcements to enhance the clout of President Obama’s antagonists. But it remains to be seen whether that will set the stage for two years of continuing conflict, or open a door to compromise as both parties seek to lay the groundwork for the 2016 presidential race. Here is a look at some of the lawmakers who will probably play key roles in the 2015 congressional battles:

The hard-liners

Texas Sen. Ted Cruz usually grabs most of the attention on the Republican side, but look for Utah Sen. Mike Lee to step out of that shadow as a prominent leader of the Tea Party wing. Lee was Cruz’s chief ally in past showdowns, such as the effort to defund President Obama’s health care law and his executive actions on immigration. Both issues are sure to be on the agenda this year.

After unseating a moderate Republican incumbent in 2010, Lee has worked to develop a conservative policy platform. But the 114th Congress will test Lee and his conservative convictions as members of Republicans’ establishment wing consider a 2016 primary campaign against him in his solidly Republican state.

For Democrats, the next two years may be judged by how Sen. Elizabeth Warren wields her influence with the party’s progressive base. Until recently, she’d largely followed the traditional low-profile route for new senators. But the fight in November over a major spending bill, which included eleventh-hour changes to relax banking regulations, prompted Warren to take a leading role against the deal.

Warren has a new, somewhat informal leadership title for the Democrats as they become the Senate’s party for the first time in eight years. She says she is not running for president in 2016, but hasn’t slammed the door shut in the way Hillary Clinton and other would-be Democratic presidential candidates might like.

 

The insiders

Republican Sen. Rob Portman of Ohio has been a behind-the-scenes player in Washington for years - including six terms in the House and two years in George W. Bush’s administration as trade representative, and then budget director. He was on Mitt Romney’s short list for vice president in 2012 and considered a 2016 presidential candidacy of his own before announcing last month that he would focus instead on running for re-election to the Senate.

Incoming Majority Leader Mitch McConnell was among the happiest with Portman’s decision. Not only does it mean McConnell probably doesn’t need to worry about Republicans losing the Senate seat in 2016, it also frees Portman to help advance party priorities. Portman’s background makes him a natural for helping to guide the budget-writing process that will consume Washington for much of the early part of the year. He’ll also have a seat at the table for talks about tax reform.

With outgoing Senate Majority Leader Harry Reid inclined to focus on his own 2016 re-election fight, Sen. Charles Schumer will take on more responsibility in managing how Democrats adjust to their new status in the minority. Schumer has worked to build bridges with Republicans while being one of his party’s primary political strategists. The New York Democrat is seen as Reid’s most likely successor, but the elevation of Sen. Elizabeth Warren into the leadership showed the challenges Schumer will face in leading a caucus with an increasingly vocal progressive wing.

 

The swing-state senators

Republicans’ successful election night gave the party a slightly bigger cushion in the upper chamber than many expected—54 seats. That could be crucial, considering that the 2016 election map favors Democrats because of the high number of Republican incumbents facing re-election in states that Democrats have carried consistently in recent presidential election years.

Illinois Sen. Mark Kirk, who won the seat Obama vacated to become president, could be the most vulnerable. Kirk has forged a reputation as a moderate Republican during multiple terms representing the Chicago suburbs in the House and during his first term in the Senate. Whether that continues to suit state voters, and whether he can mount a vigorous campaign as he continues to recover from a stroke, will be key to whether Republicans can hold their majority into the next presidential administration.

Sen. Michael Bennet of Colorado is one of the few Democratic incumbents who will run in a competitive state in 2016. He was appointed to the seat, then won a tough election fight in the GOP-friendly year of 2010. The 2014 Democratic losses were tough on him because of his role as the party’s campaign committee chairman.

 

The Leaders

Rep. Kevin McCarthy begins his first full term as the House majority leader this week after Rep. Eric Cantor’s primary election loss last June led to a promotion for the five-term California congressman.

His more low-key and back-slapping style has been received warmly among the Republican rank and file, but that doesn’t mean he’s been able to avoid the internal party divisions that vexed his predecessor. The real test for McCarthy in the new Congress will be to demonstrate that he has as much heft in policy as he has in politics.

Democratic Rep. Ben Ray Lujan of New Mexico is among the few new faces in the House Democratic leadership next year, assuming the role of chairman of the Democratic Congressional Campaign Committee. House Minority Leader Nancy Pelosi, D-Calif., enlisted the 42-year-old as the party ponders its direction. Democrats are starting 2015 with the fewest House seats since 1949. Lujan’s primary job will be helping to put Democrats within striking distance of regaining the House majority heading into 2016, but he’ll also provide a voice for newer members at the leadership table.