The 77-year-old's decision sets up one of the biggest primaries of the year as Democrats seek to finally oust GOP Sen. Susan Collins.

Maine Gov. Janet Mills is expected to launch a campaign on Tuesday to unseat longtime U.S. Susan Collins, R-ME, according to internal campaign documents and a now-deleted social…

The 77-year-old's decision sets up one of the biggest primaries of the year as Democrats seek to finally oust GOP Sen. Susan Collins.

Maine Democratic Gov. Janet Mills announced that she will be running for U.S. Senate in an effort to unseat Republican Sen. Susan Collins.

Maine's Senate race will be one of the most closely watched races in next year's midterms. Mills will first square off with fellow Democrat Graham Platner.

Many leading progressive senators are sitting on the sidelines despite their leaders backing Maine Gov. Janet Mills, who jumped into the race this week.