Sen. Susan Collins, R-Maine, could face a tough re-election battle this year, due to poor approval ratings and pressure amid the Trump impeachment trial. 

Collins, 67, is considered the most moderate Republican in the Senate, hailing from a state which typically votes for Democrats in presidential elections. 

Collins has won by wide margins in every election since 1996 and is known for breaking from her party. She voted to acquit former President Bill Clinton in 1999 during his Senate impeachment trial and is pro-choice. She also has voiced support for LGBT issues and gay marriage.

Yet, Collins made a controversial vote in favor of appointing Judge Brett Kavanaugh to the Supreme Court in 2018, a decision which has dismayed liberals. Kavanaugh had been accused of sexually assaulting Christine Blasey Ford while in high school, with Ford speaking to Congress on the matter. 

The vote led her Maine Democratic opponent, State House Speaker Sara Gideon, to outraise Collins this summer. Gideon raised $3.2 million between July 1 and Sept. 30, while Collins saw $2.1 million in donations. 

Collins is under even more pressure as the Senate impeachment trial of President Trump commences. If Collins votes against witnesses being called during the trial, or for acquitting Trump of his impeachment charges, it would anger liberals in her state and possibly hurt her reelection chances. 

If Collins votes for witnesses to be called or for convicting the President, it could draw criticism from her own party and infuriate Trump. 

Collins told NBC affiliate WCSH Saturday that she “is very likely to vote for additional information” in the impeachment trial. If witnesses during the Senate trial present compelling testimony, it could influence whether Trump is convicted and removed from office. 

The Senate trial began this week, with Chief Supreme Court Justice John Roberts swearing-in senators. Congressional elections are set for Nov. 3.