A handful of races will decide whether Mitch McConnell and the GOP can keep their grip on the Senate next year – including in Alabama, where Roy Moore, accused of sexual misconduct with teen girls decades ago, is again running for the Republican nomination. President Donald Trump faces a grind to win another term in the White House. Even if he stays another four years, Democrats appear favored to keep the House — and the oversight and policy headaches it can cause Trump. So Republicans will count on holding their Senate majority. The chamber has mostly given Trump refuge — confirming his judicial and executive branch nominees and taking up minimal legislation — since Democrats took House control back in January.

Despite a favorable 2020 map for Democrats, the GOP appears to have the edge in holding the Senate. Republicans start with a 53-47 majority, so they would have to lose a net four seats to yield control of the chamber. The GOP has to defend 22 seats, while elections will take place for 12 Democratic-held seats. Recruiting troubles have only hampered Democrats more. Several potentially formidable candidates declined to run for Senate: former Georgia House Minority Leader Stacey Abrams, Montana Gov. Steve Bullock, former Colorado Gov. John Hickenlooper and former Rep. Beto O'Rourke of Texas. Bullock, Hickenlooper and O'Rourke ran for president. Here are key races that will shape the fight for the Senate in 2020:

Alabama, Democratic Sen. Doug Jones:

Democratic Alabama U.S. Senate candidate Doug Jones and wife Louise acknowledge supporters at the election night party in Birmingham, Alabama, December 12, 2017. Marvin Gentry | Reuters

Just about any path Democrats can take toward Senate control would rely on Jones holding his seat. Challengers have lined up to try to take the senator down in deep red Alabama in one of the GOP's best chances to flip a seat. Rep. Bradley Byrne, R-Ala., is the mainstream GOP favorite running in the Republican primary. State Rep. Arnold Mooney and former college football coach Tommy Tuberville have also jumped into the race on the GOP side. But one candidate upended the Alabama Senate contest Thursday. Moore — the former state Supreme Court chief justice who lost to Jones in a close December 2017 special election amid accusations of sexual misconduct — entered the race over Trump's objections. Republicans worry a Moore primary win would give Jones his best chance to win a full six-year term in the Senate. The Senate Republican campaign arm has criticized him. Trump, who backed Moore in the 2017 election, has said the former judge "cannot win" in 2020. Jones beat Moore by about 1.5 percentage points in the 2017 special election to replace Jeff Sessions, who left the Senate to become Trump's attorney general. Jones has tried to build a centrist reputation in the Senate. While he has voted for some Trump nominees for Cabinet positions and backed GOP-written bills, he has mostly aligned with mainstream Democrats on issues such as abortion and immigration.

Arizona, Republican Sen. Martha McSally:

Martha McSally, Republican U.S. Senate candidate from Arizona, speaks during an election night rally in Tempe, Arizona, on Tuesday, Aug. 27, 2018. Caitlin O'Hara | Bloomberg | Getty Images

McSally lost a Senate race last year. She hopes this time will end differently. The senator took office this year after her appointment to finish the late Sen. John McCain's term. McSally will likely face Mark Kelly, the former astronaut backed by national Democrats, in next year's election. She faces a slog to keep the seat in a state that has grown more favorable for Democrats. Trump has only complicated matters for McSally. Last month, Trump threatened to slap 5% tariffs on all Mexican imports before deciding against the move. At the time, McSally said she does "not support these types of tariffs, which will harm our economy and be passed onto Arizona small businesses and families." The duties would disproportionately damage Arizona: The border state gets about 40% of its imports from Mexico, the highest share for any state. While Arizona dodged potential calamity for now, Trump has not ruled out putting tariffs on America's southern neighbor if it does not do enough to curb migration. Kelly, the husband of former Rep. Gabby Giffords — a Democrat who was left with brain damage following a 2011 shooting at a public event — has run on issues including health care and gun control. Republicans have tried to tie him to liberal policy plans such as "Medicare for All" and the Green New Deal, which could deter some voters in the swing state. (Kelly has said he opposes Medicare for All and supports a public health care option. He has also said he does not back a Green New Deal). Sen. Kyrsten Sinema, D-Ariz., beat McSally by about 2.5 percentage points in the state's U.S. Senate race last year.

Colorado, Republican Sen. Cory Gardner:

Sen. Cory Gardner Bill Clark | CQ Roll Call | Getty Images

Gardner has perhaps the toughest path to reelection of any Republican senator next year. Democrats are jumping to get the chance to challenge him. At least nine Democrats have jumped into the primary race in Colorado, a state that has moved away from Republicans. Contenders for the nomination include former Colorado House Speaker Andrew Romanoff, former U.S. Attorney John Walsh, former state Sen. Mike Johnston and former Obama administration official Dan Baer. Crowded primaries often bring concerns about a nominee entering a general election bruised or having taken policy positions that may not appeal to voters outside of a candidate's party. Democrats lost out on one potentially strong recruit in the state. Former Gov. John Hickenlooper, who won a statewide race as recently as 2014, ran for president after Democratic leaders pushed him to make a Senate bid. Before he made his presidential run official, Hickenlooper told Politico in February that "I'm not cut out to be a senator." Gardner has pushed to build a centrist reputation by working with Democrats on issues such as immigration and marijuana. Still, he sided with Trump on one major immigration vote: whether to overturn the president's national emergency declaration over migration at the southern U.S. border. Democrats hope to extend a blue shift in Colorado. In last year's midterms, Democratic Gov. Jared Polis won by about 10 percentage points. Democratic Rep. Jason Crow, meanwhile, handily defeated incumbent GOP Rep. Mike Coffman.

Georgia, Republican Sen. David Perdue:

Sen. David Perdue (R-GA) speaks as (L-R) Sen. Todd Young (R-IN), Sen. Dean Heller (R-NV), Sen. Shelley Moore Capito (R-WV), Sen. Michael Rounds (R-SD) and Secretary of the Treasury Steven Mnuchin listen during a news conference on tax reform November 7, 2017 on Capitol Hill in Washington, DC. Getty Images

Democrats also lost out on a top Senate recruit in Georgia. The party felt former state House Minority Leader Stacey Abrams would have the best chance to knock off Perdue in the red state. But Abrams, who lost a close gubernatorial race last year, declined to run in late April. At the time, she said "my responsibility is not simply to run because the job is available. I need to run because I want to do the job." She added that she would do "everything in [her] power" to make sure the state elects a Democratic senator. So who wants to run for the seat? Former Columbus Mayor Teresa Tomlinson has joined the race. She has a difficult task in trying to unseat Perdue in the Republican-leaning state. The staunch Trump ally won his first term in 2014 in an eight-percentage point victory. A sustained trade war with China could also affect the Georgia race. Chinese tariffs on U.S. goods have affected industries such as soybeans, peanuts and cotton.

Maine, Republican Sen. Susan Collins

Sen. Susan Collins (R-ME) speaks to reporters as she arrives for a nomination vote on Capitol Hill in Washington, December 13, 2017. Joshua Roberts | Getty Images

Despite Maine's swing state status, unseating Collins may prove tough for Democrats. The senator, who often breaks with the GOP, has enraged people on both the left and right with her votes in the last two years. Opponents have lined up in the 2020 Senate race. Pro-Trump Republican blogger Derek Levasseur will challenge Collins in the primary. Meanwhile, lobbyist and unsuccessful 2018 gubernatorial candidate Betsy Sweet and lawyer Bre Kidman will run on the Democratic side. Collins notably helped to sink a Republican plan to dismantle the Affordable Care Act in 2017, earning the ire of conservatives. Then last year, she deflated Democrats' hopes by voting to confirm Supreme Court Justice Brett Kavanaugh. Democrats fared well in Maine last year. They flipped the governor's mansion and a key U.S. House seat. But Collins poses a different challenge. She won her last election in 2014 by nearly 40 percentage points. The senator will likely have much more money at her disposal than her challengers throughout the contest.

Michigan, Democratic Sen. Gary Peters:

Sen. Gary Peters, D-Mich. Bill Clark | CQ-Roll Call Group | Getty Images

Peters will have a tougher time than most Senate Democrats in keeping his seat next year. He will have to run in a state Trump won in 2016 against a candidate many Republicans consider the GOP's best recruit. John James, a businessman and Army veteran, will try to knock off Peters in 2020. He challenged Democratic Sen. Debbie Stabenow in Michigan last year and lost by more than 6 percentage points. Republicans hope Peters' relative anonymity will help make next year's race closer. In April, 43% of Michigan voters said they had never heard of Peters, according to Morning Consult polling. That makes him less well known than any other senator, the surveys found. Trump and James will look to replicate the president's 2016 success in Michigan. Before Trump, a Republican had not won the state since 1988. Still, he squeaked out a win there by only about 10,000 votes. Democrats fared better in Michigan last year. Democratic Gov. Gretchen Whitmer won by about 10 percentage points. The party also flipped two GOP-held House seats in the state.

New Hampshire, Democratic Sen. Jeanne Shaheen:

U.S. Senator Jeanne Shaheen (D-NH) seen speaking during a program titled 'Tracking Federal Funding to Combat the Opioid Crisis' at the Bipartisan Policy Center in Washington, DC. Michael Brochstein | SOPA Images | LightRocket | Getty Images

Pundits consider Shaheen a clear favorite to keep her seat. Still, the Senate race could become competitive in the traditional swing state. Trump lost New Hampshire in 2016 by only about 0.3 percentage points. Democratic Sen. Maggie Hassan won even more narrowly, defeating incumbent GOP Sen. Kelly Ayotte by roughly 1,000 votes. Still, Shaheen has shown herself as a formidable candidate. In 2014, she beat former Republican Massachusetts Sen. Scott Brown by about 3 percentage points during a strong year for the GOP. She has strong name recognition and one of the highest approval ratings among senators up for reelection next year, according to Morning Consult polling. The senator's fate will depend on whom Republicans can get to run against her. GOP Gov. Chris Sununu, seen as a potentially tough opponent for Shaheen, declined to run in May. It is unclear who else could challenge the incumbent.

North Carolina, Republican Sen. Thom Tillis:

Sen. Thom Tillis, R-N.C., attends a Senate Veterans' Affairs Committee hearing in Russell Building titled 'Fiscal Year 2020 Budget for Veterans' Programs and Fiscal Year 2021 Advance Appropriations Request,' on Tuesday, March 26, 2019. Tom Williams | CQ-Roll Call Group | Getty Images

Trying to navigate both primary challengers and a growing field of Democratic rivals, Tillis has leaned into staunch support for Trump. While the strategy may boost him against Republicans, it could put him in a more difficult position in a swing state general election. In echoes of GOP primaries across the country last year, North Carolina's Republican Senate candidates have already clashed over their support for Trump. Tillis' campaign has already targeted one challenger — businessman Garland Tucker — over his resistance to Trump's presidential nomination in 2016. Another Tillis primary opponent, businesswoman Sandy Smith, contends the senator has not done enough to support Trump. Candidates who have jumped into the Democratic primary hoping to take on Tillis include former state Sen. Cal Cunningham and state Sen. Erica Smith. Cunningham has touted the endorsement of former Democratic U.S. Sen. Kay Hagan — whom Tillis defeated to win his seat in 2014. While Trump won North Carolina in 2016 and the state has two Republican senators, recent statewide races there have been competitive. The president carried the state by nearly 4 percentage points in 2016, while GOP Sen. Richard Burr won by nearly 6 percentage points. But in the same year, Democratic Gov. Roy Cooper narrowly beat incumbent Republican Pat McCrory. This year, Tillis has cast some pivotal votes in favor of the president's priorities. Though a handful of Republicans joined Democrats in voting to overturn Trump's emergency declaration at the southern border, Tillis voted to uphold it. The senator has also touted his efforts to push for the confirmation of Supreme Court Justice Brett Kavanaugh last year.

Texas, Republican Sen. John Cornyn: