CAPE ELIZABETH, Maine (AP) — If there’s one story Janet Mills likes to share as a warning not to underestimate her political prowess, it’s about a blue suit that the Democratic Maine governor once wore. It was more than four decades ago and Mills, the first female prosecutor working in the state attorney general’s criminal division, secured a successful verdict in a murder trial. Yet a newspaper headline focused on a more trivial angle: “The prosecutor wore pale powder blue.” “That wasn’t the first time someone underestimated me. And it certainly wasn’t the last,” Mills, now running for U.S. Senate, wrote in a recent memo to campaign donors. The message is one the two-term governor is returning to frequently as she seeks the Democratic Senate nomination to take on longtime Republican Sen. Susan Collins. Despite having decades in public office and the support of the party establishment in Washington, she’s back to being the underdog ahead of the first Democratic primary debate next week.…