Mitch McConnell (R-Ky.), left, who is set to become the next Senate majority leader, with Sen. John Barrasso (R-Wyo.) and Sen. John Cornyn (R-Tex.). (Mark Wilson/Getty Images)

House and Senate lawmakers return to the Capitol on Wednesday to start the process by which Republicans will begin to carve up the spoils from their midterm-election rout, while Democrats do battle over the leftover kernels of power available to the minority party.

There will be leadership elections in both parties in both chambers, and the contenders for the top jobs are unchallenged, for now, making them overwhelming favorites.

But a small collection of contested and contentious races on the undercard could provide initial clues about the shifting internal party politics on Capitol Hill and how those changes may affect the country.

Mitch McConnell (R-Ky.), fresh off a resounding victory in his reelection campaign, faces no challenger to his elevation to Senate majority leader. The promotion is set to come after eight years as minority leader and four prior failed attempts at winning the majority.

House Speaker John A. Boehner (R-Ohio), after another ­double-digit gain in seats, also faces no challenge, which probably means that he will be just the second Republican since the Great Depression to secure a third term in the powerful post.

The GOP gained control of the Senate in the midterm elections, taking hold of the legislative agenda in that chamber. Here are three of the policies Republicans are likely to tackle as they take the reins in January 2015. (Julie Percha/The Washington Post)

Democrats are expected to reelect Sen. Harry M. Reid (Nev.) as their leader, this time in the minority. He has spent a full decade as his party’s top senator. If he serves through 2016, Reid would become the second-
longest-serving Democratic leader
in Senate history. House ­Minority Leader Nancy Pelosi (Calif.) is expected to win another term as the top Democrat. She has already spent eight years as leader of the opposition (sandwiched around her four years as speaker).

The other higher-level leaders, such as House Majority Leader Kevin McCarthy (R-Calif.) and House Minority Whip Steny H. Hoyer (D-Md.), also are running uncontested. Several lower-level battles in the four caucuses provide the real palace intrigue.

In the House, each party must choose someone to run its campaign committee. In the weeks leading to the Nov. 4 elections, Reps. Roger Williams (R-Tex.) and Aaron Schock (R-Ill.) began positioning themselves to challenge the incumbent, Rep. Greg Walden (R-Ore.), arguing that Republicans were going to win only a few seats in a midterm climate favorable for the GOP nationwide. Instead, the National Republican Congressional Committee delivered its second double-digit gain in three election cycles, giving Walden more to crow about in his reelection bid.

For Democrats, Rep. Steve Israel (N.Y.) is retiring as chairman of the Democratic Congressional Campaign Committee, a position that Pelosi appoints, after four years atop the panel.

A collection of Democratic lawmakers who have served several terms have been in the mix for the post, including Reps. Donna F. Edwards (Md.), Jim Himes (Conn.) and Jared Polis (Colo.), but in recent days some have suggested that it’s time to turn the page and perhaps skip a generation.

Reps. Joe Kennedy (D-Mass.), the 34-year-old grandson of Robert F. Kennedy, and Joaquin Castro (D-Tex.), the 40-year-old twin brother of Housing and Urban Development Secretary Julian Castro, are under consideration even though they have yet to finish their first terms in office, Politico reported Monday.

Such a move would draw parallels with Pelosi’s decision after the 2004 elections, in which Republicans added to their House majority, to hand over the DCCC to Rahm Emanuel (Ill.), who was finishing his first term in Congress.

Emanuel, who later became the White House chief of staff and now is Chicago’s mayor, delivered a 30-seat victory and the majority in 2006.

The most significant fights inside each caucus might be the battles for top committee posts. Rep. Paul Ryan (Wis.), ending an eight-year run as the leading Republican on the Budget Committee, is the strong favorite to win the chairmanship of the Ways and Means Committee, given his considerable clout after his 2012 stint as vice-presidential nominee, but first he must secure the votes over Rep. Kevin Brady (Tex.), who has more seniority on the panel.

Republicans have a three-way battle for the gavel for the Oversight and Government Reform Committee, where the current chairman, Rep. Darrell Issa (Calif.), has reached his six-year limit. The most aggressive candidate, Rep. Jason Chaffetz (Utah), has been active in recent investigations of security breaches involving the Secret Service, while two Ohioans, Reps. Jim Jordan and Michael R. Turner, are angling for the gavel as well.

Democrats seeking the ranking member slot on the vaunted Energy and Commerce Committee are engaged in a fierce battle that is shaping up as a proxy fight over how much clout Pelosi retains. Pelosi has thrown her full support behind the candidacy of Rep. Anna G. Eshoo (Calif.), who will be the leader’s closest friend in Congress next year.

“Once again, I am writing to enthusiastically endorse Anna Eshoo,” Pelosi wrote Monday afternoon in her latest “dear colleague” missive in support of her friend. The retirements of Reps. Henry A. Waxman (D-Calif.), who is leaving his top Energy Committee post, and Rep. George Miller (D-Calif.), who is departing his post atop the Education and the Workforce Committee, have depleted California’s power in the House, making Eshoo’s bid something akin to a last stand for the Golden State.

But Rep. Frank Pallone Jr. (D-N.J.) has more seniority than Eshoo and has the backing of many veteran Democrats, such as Hoyer and members of the Congressional Black Caucus, where seniority has been often viewed as sacrosanct.

Pallone is a stout liberal with no real policy differences from Eshoo, but Pelosi’s involvement has turned the race into a chance for those who are unhappy with her continued leadership, after three straight failed elections, to express displeasure with her by opposing Eshoo.

Senate Republicans also have a tough vote Thursday in selecting their top political strategist, for the chairmanship of the National Republican Senatorial Committee. The two candidates, Sens. Dean Heller (Nev.) and Roger Wicker (Miss.), come from different regions and different congressional generations.

Wicker, 63, was first elected to Congress in 1994, and he had a 13-year run in the House before moving to the Senate. “I can draw on my experience and wide array of relationships for the good of our party, the committee, and our country. And I am fully prepared to give the time, energy and resources needed,” Wicker wrote in an e-mail to colleagues the morning after the party secured the Senate majority.

Heller, 54, has been in the Senate for just over three years and before that served less than five years in the House. If Republicans side with Heller, his first priority will be recruiting from his home state a top-flight challenger to Reid, who is up for reelection in 2016.

The domino effect came into play in the competition for the chairmen’s gavels over the weekend when Sen. Charles E. Grassley (R-Iowa) announced his intention to stay on the Judiciary Committee as chairman rather than seek the top spot on the Finance Committee. That assures the ascension of Sen. Orrin G. Hatch (R-Utah) to wield the gavel on that powerful panel, and Sen. John McCain (R-Ariz.) is set to become chairman of the Armed Services Committee.

Senate Democrats appoint — rather than elect — the chairman of the Democratic Senatorial Campaign Committee. Reid is facing a generational choice similar to that of House Democrats.

Those under consideration include a host of senators who first won election in 2006, including Sherrod Brown (Ohio), Amy Klobuchar (Minn.), Jon Tester (Mont.), Sheldon Whitehouse (R.I.) and Claire McCaskill (Mo.). And several relative newcomers also are mentioned as possible chairmen: Christopher A. Coons (Del.) and Kirsten Gillibrand (N.Y.).

Gillibrand, like other rising Democratic stars including Sens. Cory Booker (N.J.) and Elizabeth Warren (Mass.), has said she is not interested, but Reid has successfully prevailed on senators in the past to take the grueling job.