Gov. Janet Mills (D-ME) announced her long-expected candidacy Tuesday for the Maine Senate seat held by Sen. Susan Collins (R-ME), teeing up a perennial high-stakes battleground race against two longtime politicians with broad name recognition.

The campaign by Mills, 77, exposes a trend this cycle of Senate Democrats’ establishment wing relying on an older string of candidates to carry the party’s long-shot quest of retaking the upper chamber.