LIVE UPDATES: Sara Gideon secures the Democratic nomination to face Sen. Susan Collins in Maine

• Maine is holding congressional primary elections on Tuesday, July 14.
• Three candidates are vying for the Republican nomination to face Rep. Jared Golden in Maine's second district, a top battleground district Democrats won back in 2018.
• Maine uses a ranked-choice voting system, meaning that the race could go to an additional ranked-choice runoff between the top two candidates if no one earns a majority of the vote outright.

Polls closed at 8 p.m. Eastern Time in Maine.

The races:

Sara Gideon, the Speaker of the Maine House of Representatives, easily defeated her opponents, lawyer Bre Kidman and activist Betsy Sweet, to clinch the Democratic nomination for US Senate to face GOP Sen. Susan Collins in the fall.

The race between Collins, a four-term Senator, and Gideon, is expected one of the most competitive races of 2020 that will determine which party controls the chamber.

There's also a competitive Republican primary in Maine's second congressional district to face Rep. Jared Golden, a former state legislator and US Marine veteran who defeated a Republican to flip the seat to Democratic control in the 2018 midterm elections.

Maine's second district, which occupies most of the state's geographical landmass and is heavily rural and working-class, flipped from voting for former President Barack Obama by 9 percentage points in 2012 to vote for President Donald Trump by 10 points in 2016.

In addition to winning the seat back for Democrats, Golden was also the first member of the House elected with Maine's relatively new ranked-choice voting system for federal elections.

In most US elections, a voter only casts a vote for one candidate on their ballot, and the candidate who earns the most votes wins outright.

But in Maine's system, voters rank all the candidates on the ballot based on the order of their preferences. If no candidate earns over 50% of the vote outright, the lowest-performing candidate is eliminated, and the race goes to a ranked-choice runoff. For voters whose first-choice candidates did not advance, ballots are re-tallied and those voters' second-choice selections are redistributed until a candidate earns a majority of the vote.

State Senator Eric Brakey, former Maine State Representative and Lisbon, ME town councilmember Dale Crafts, and Adrienne Bennett, a realtor who previously served as press secretary to former GOP Gov. Paul LePage, are the Republican candidates vying for the nomination to face Golden.

A poll of the race conducted by SurveyUSA on behalf of FairVote showed Crafts in the lead over his opponents, with 37% of likely Republican primary voters indicating they would pick Crafts as their first choice followed by Bennett at 25%, Brakey at 19%, and 19% undecided.

The race between Golden and the eventual Republican nominee will be a hotly-contested one. Election handicappers including the Cook Political Report and Sabato's Crystal Ball at the University of Virginia have rated the race as a tossup while Inside Elections rates it as leaning Democratic.

Maine's second district also plays an important role in the electoral college, and will receive a significant amount of attention in the presidential race. Maine, along with Nebraska, allocates its electoral college votes proportionally, with two allocated based on the statewide results and each congressional district accounting for one electoral college vote.

In the electoral college, Maine's second district is rated as a tossup by the Cook Political Report, tilt Republican by Inside Elections, and lean Republican by Sabato's Crystal Ball.