WASHINGTON — Voting got underway on Tuesday across the United States as Americans make the final choice as to who will be their president for the next four years: Donald Trump or Joe Biden.

The world will be watching as votes are cast and the results begin pouring in, with one eye placed firmly on the large swing states such as Pennsylvania, Ohio, and the ever-crucial Florida.

More than 100 million Americans cast their ballots before polls opened, shattering records and likely reducing the number of people who will turn out to vote in person this year.

As the polls opened, Republicans in the key battleground state of Pennsylvania filed a federal lawsuit that took aim at how election officials in Democratic-leaning Montgomery County handled absentee ballots that arrived before Election Day.

The plaintiffs allege officials in this suburban Philadelphia county conducted "pre-canvassing" of ballots before 7 a.m. ET Tuesday and allowed people to fix perceived defects in their ballots. The Republicans want any changed ballots set aside.

In and around polling places across the US, voters were greeted by reminders of an election year shaped by a pandemic, civil unrest, and bruising political partisanship. Many wore masks to the polls — either by choice or by official mandate — with the coronavirus raging in many parts of the country.

The most closely watched results will start to trickle in after 7 p.m. ET (12 a.m. GMT), when polls close in states such as Georgia, though definitive national results could take days if the contest is tight.

Biden entered election day with multiple paths to victory while Trump, playing catch-up in a number of battleground states, had a narrower but still feasible road to clinch 270 electoral college votes.

Control of the Senate is at stake, too — Democrats need to net three seats if Biden captures the White House to gain control of all of Washington for the first time in a decade. The House is expected to remain under Democratic control.