Graham Platner prevailed in the Maine Democratic Senate primary, breaking 50% of the vote and clinching the nomination to face Sen. Susan Collins, a Republican who national Democrats hope to topple on their way to recapturing control of the Senate in November. Platner had 75 percent of the votes with only 8 percent of the ballots counted when the Associated Press called the race on Tuesday evening, suggesting a dominant performance. Maine Gov. Janet Mills, had just 19 percent.