State Sen. Katherine ClarkKatherine Marlea ClarkDems vow to repeal parts of GOP tax law Five things to watch for in Trump’s State of the Union Overnight Health Care: Bipartisan health plan faces new challenge from conservatives MORE (D) won the special election for Sen. Ed Markey's (D-Mass.) old House seat on Tuesday night.

Clark easily won the race, with 88 percent of precincts reporting, she led Republican Frank Addivinola 68 percent to 30 percent, The Washington Post reported.

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Massachusetts' 5th District is deeply Democratic, and the party never feared Clark losing to Addivinola.

After winning a seven-way primary with a third of the vote, Clark kept a low profile, engaging in only one debate with her opponent and planning few campaign stops in the final weeks of the race.

She received the backing of EMILY's List and Massachusetts Attorney General Martha Coakley.