Democratic Rep. Chris Pappas defeated former GOP Sen. John Sununu in the New Hampshire Senate race, AP projects, becoming the first openly gay man elected to the U.S. Senate.

Why it matters: Pappas' victory keeps the seat in Democratic hands and could boost the party's chances of taking control of the Senate.

Driving the news: Pappas led Sununu 61% to 38% with 20% of the votes counted.

He'll succeed retiring Sen. Jeanne Shaheen (D-N.H.) in January.

Catch up quick: Republicans saw New Hampshire as a top pickup opportunity, with Senate Majority Leader John Thune campaigning for Sununu in the competitive race, despite polls showing Pappas ahead.

Most polls compiled by the New York Times in the weeks before Election Day showed the Democratic Pappas leading Sununu by 5 to 8 percentage points.

Zoom in: Although President Trump endorsed him, Sununu has shown daylight with the president, criticizing his trade war with Canada and his so-called anti-weaponization fund — and he backed Trump's primary opponents in…