Washington (CNN) A leadership shakeup is coming to the House of Representatives after Democrats won enough seats to take back the lower chamber of Congress from Republicans in this year's midterms.

Nancy Pelosi faces her first major test in her bid to become the next House speaker when House Democrats hold a closed-door vote on Wednesday to elect a nominee. Pelosi is expected to easily prevail, but a final vote on the House floor won't take place until January.

It is still not clear if she has the votes to win in January, but no challenger has emerged to oppose her and Pelosi and her allies continue to project confidence that she will have no issue winning the gavel.

House Majority Leader Kevin McCarthy walks out of the caucus room in October 2015 on Capitol Hill. (Photo by Chip Somodevilla/Getty Images)

Republicans have already held their leadership elections and chose California Rep. Kevin McCarthy to serve as the No. 1 House Republican in the next session of Congress, when Democrats control the lower chamber.

Here's an overview of the top leadership positions and who is vying for what role:

House Minority Leader Nancy Pelosi holds a news conference following the 2018 midterm elections at the Capitol Building on Tuesday in Washington.

The Democratic leadership contest

HOUSE SPEAKER

Nancy Pelosi wants to become House speaker -- again.

The longtime House Democratic leader, who served as the first and so far only female House speaker from 2007 to 2011, isn't facing any challenge at the moment.

Pelosi has repeatedly expressed confidence that she will be elected to the position . There is a small and vocal contingent of House Democrats who have called for new leadership, and several of them have pledged to vote against her for speaker. But the opposition to Pelosi has suffered several setbacks, the most prominent being when Rep. Marcia Fudge of Ohio, who had been publicly weighing the possibility of entering the speaker's race, announced that she would instead back Pelosi.

Rep. Marcia Fudge speaks during the Leading Women Defined: Women On Washington in March 2013 in Washington, D.C.

In January, Pelosi will need to shore up votes from most of the House Democratic caucus to win the final vote on the House floor, which traditionally has a threshold of 218 votes -- an absolute majority of all members of the House -- but could be won with fewer.

The House speaker wields considerable power in the lower chamber, including the ability to shape the agenda on the House floor by determining which bills come up for debate and a vote and which ones do not.

The House speaker is second in the line of presidential succession after the vice president.

House Minority Whip Steny Hoyer, a Maryland Democrat, leaves the House of Representatives Chamber in January in Washington.

MAJORITY LEADER

Rep. Steny Hoyer, who currently holds the position of No. 2 House Democrat as minority whip, has launched a bid to become the majority leader in the next Congress.

Like Pelosi, Hoyer is a veteran of House Democratic leadership. The Maryland Democrat has served as second-highest ranking Democrat after Pelosi for 16 years and in lower-level Democratic leadership positions even longer.

The majority leader is responsible for managing the schedule that determines when legislation will be considered on the House floor and planning the legislative schedule on a daily, weekly and monthly basis. The majority leader also works with committee chairs on policy and to bring bills that have advanced out of committee -- and have the support of leadership and the votes to pass -- to the House floor.

Rep. Jim Clyburn, a South Carolina Democrat and Assistant Democratic Leader, is pictured.

MAJORITY WHIP

Rep. James Clyburn, who currently holds the No. 3 Democratic leadership spot of assistant Democratic leader, is running for majority whip.

Clyburn, a lawmaker from South Carolina, is a member of the Congressional Black Caucus, a key voting bloc among House Democrats, and is the highest-ranking African-American member of the House.

Rep. Diana DeGette of Colorado, who serves on the Democratic whip team as a chief deputy whip, had been challenging Clyburn for the position, but she dropped her bid in mid-November, clearing the path for Clyburn to win.

The majority whip acts as a key vote counter for party leadership and is tasked with figuring out how much support a particular bill will have if it comes to the floor for a vote. The whip also works to mobilize votes in support of leadership priorities.

ASSISTANT DEMOCRATIC LEADER

Several Democrats are running for assistant Democratic leader, a position in the Democratic leadership hierarchy created after Democrats lost the House to Republicans in the 2010 midterms.

Ben Ray Luján, the chair of the House Democratic campaign arm, is running for the post. Rep. David Cicilline of Rhode Island had been challenging him for the position, but announced in mid-November that New Mexico Rep., the chair of the House Democratic campaign arm, is running for the post. Rep.of Rhode Island had been challenging him for the position, but announced in mid-November that he would instead run for a newly created role of chair of the Democratic Policy and Communications Committee.

Rep. Cheri Bustos of Illinois had been vying for the position as well, but dropped her bid after Luján's entry into the race; she began running instead to lead the campaign arm, the Democratic Congressional Campaign Committee.

CAUCUS CHAIR

Hakeem Jeffries, a Democrat from New York, and Rep. Barbara Lee of California, both members of the Congressional Black Caucus, Rep.a Democrat from New York, and Rep.of California, both members of the Congressional Black Caucus, are competing for the spot of chair of the House Democratic Caucus.

Rep. Linda Sánchez of California had also been running for the spot, but she dropped her bid, citing an "unexpected family matter" and later disclosed that her husband had been indicted in Connecticut.

The position is currently held by Rep. Joe Crowley of New York, but he won't be around in the next Congress after he was defeated in a major upset by progressive primary challenger and political newcomer Alexandria Ocasio-Cortez.

Republican leadership in the next Congress

MINORITY LEADER

Rep. Kevin McCarthy, the current No. 2 Republican and House majority leader, will be the top Republican leader in the next Congress. McCarthy was picked by House Republicans in a closed-door election held the week after midterms to be the Republican minority leader, taking over from Paul Ryan as the leader of the Republican conference. McCarthy easily defeated Rep. Jim Jordan, the co-founder of the conservative House Freedom Caucus, who challenged him for the position.

The position of minority leader is the highest in the House for the party out of power. The minority leader is the most visible face of the minority party in the lower chamber and works to advance the party's objectives, despite being shut out of control of the House -- with the ultimate goal of taking back the chamber.

US Majority Whip Representative Steve Scalise, Republican of Louisiana, walks through Statuary Hall at the US Capitol in September 2017, as he returns to work after being injured in a shooting at the Republican Congressional baseball team practice earlier that year.

MINORITY WHIP

Rep. Steve Scalise, the current No. 3-ranked House Republican, was elected to be the Republican minority whip in the next Congress.

Scalise is widely respected among House Republicans and gained a higher national profile after he was shot in a 2017 attack on Republican lawmakers at a congressional baseball practice.

The minority whip acts as a vote counter and also works to mobilize support and votes for or against legislation in line with the goals of party leadership.

Rep. Liz Cheney, a Wyoming Republican, speaks during a news conference in February on Capitol Hill in Washington, DC. (Photo by Alex Wong/Getty Images)

REPUBLICAN CONFERENCE CHAIR

Rep. Liz Cheney of Wyoming has been elected to serve as House Republican Conference chair.

Cheney, the daughter of former Vice President Dick Cheney, will be taking over the role from Rep. Cathy McMorris Rodgers, who has held the position in the House majority, but did not run for re-election for the same spot in the next Congress. She plans to run for a ranking member position on the Energy and Commerce Committee instead.

The GOP conference chair plays an important role in executing party communications and media strategy.