BANGOR, Maine — As Maine Democrats vie to replace Graham Platner in their state’s Senate race, abortion — a key weakness for Republican Sen. Susan Collins — is set to shape the next phase of the contest, which Democrats view as a prime pick-up opportunity. Collins, whose home state voted for Kamala Harris in the 2024 election, is considered one of the most vulnerable Republican incumbents up for election this year. She has held onto power despit…