The Maine Senate race has been simplified by today's news that Governor Janet Mills has dropped out of the contest, with over a month to go before the June 9th primary. This essentially clears the Democratic field for Graham Platner, which could be very good news for Democrats.

Mills said she had run out of money, but this may not have been the whole reason she withdrew from the race. She has been trailing Platner in the primary polling, sometimes by 30 points or more. So she could have decided to avoid ending her political career with a crushing primary defeat, instead choosing to make her exit without that stain on her legacy. But whatever her reasons, it now appears almost certain that Platner will take on sitting Senator Susan Collins in November.

Maine is one of Democrats' biggest pickup opportunities in the Senate, since the state voted for Kamala Harris in the past presidential election but still has a Republican senator. Collins tries to position herself as an independent Republican who bucks her party on occasion, but when the chips are really down and her vote is necessary (to confirm Trump's appointees or cast a crucial vote to advance the GOP agenda), she usually winds up voting her party's line. This has led to a lot of anger from Maine voters over the past decade or so, and Collins is now more vulnerable than she ever has been. Defeating an incumbent senator is incredibly hard to do, but Maine Democrats have a good chance of doing so this year.

Graham Platner is seen by the Democratic Party establishment as somewhat of a loose cannon. Senate Minority Leader Chuck Schumer was the one to personally urge Mills to run, as she was the much-preferred candidate by the party leaders. Mills had won statewide races in Maine already and was popular enough in her home state, so Schumer (and others) saw her as the best opponent to take on Collins.

Platner, however, didn't agree. The biggest drawback with Mills is that she is 78 years old. That means she'd be in her mid-80s by the end of her first term in the Senate. Democrats have a real problem with their "gerontocracy," and electing Mills to the Senate would only make it worse. Platner is only 41 years old, and is part of the "let's get some younger people in office" movement within the Democratic Party.

Platner is a neophyte -- he's never run for public office before now. He is an oyster farmer and has run on being a "regular guy" type of politician. To put it another way, he exudes authenticity. He is definitely a guy you can see yourself sitting down and having a beer with. Platner is also an unapologetic progressive. He has been endorsed by Bernie Sanders and Elizabeth Warren. Platner reacted to the news of Mills dropping out by saying: "We will defeat Susan Collins. We will go to Washington and we will start tearing down the system that for far too long has forgotten and written off the people who make Maine and this country what it is." He calls his campaign "a movement of working Mainers who are fed up of being robbed by billionaires... and who are taking back their power."

This is what scares people like Chuck Schumer, who think that a centrist would have a better chance of winning the race. But so far, Platner has been doing pretty well with Maine voters, if the polls can be believed.

In head-to-head polling, Mills was running neck-and-neck with Collins. In polls conducted this year, three of them showed Mills winning (but just barely), two of them showed Collins winning (also just barely), and two of them showed the race was tied.

Platner, on the other hand, has led every head-to-head poll against Collins this year, often by a significant amount (in the average of the last three polls taken, Platner leads Collins by a margin of 49 percent to 42 percent).

It bears mentioning that Platner is not without flaws. He does have some serious baggage that will be hammered upon by Collins. But Mills already tried doing just that and failed to blunt his appeal to the voters, so it remains to be seen how effective this will turn out to be.

Schumer and Senator Kirsten Gillibrand (who leads the Senate Democrats' campaign organization) put out a joint statement endorsing Platner: "After years of allowing Trump's abuses of power, Senator Collins has never been more vulnerable, and we will work with the presumptive Democratic nominee, Graham Platner, to defeat her." Mills didn't mention Platner in her announcement today, and (so far) has not endorsed him. Which may not make much of a difference, since he's already got the Democratic primary pretty much sewn up.

There is one last note of caution that needs to be mentioned here. Platner's average-guy personality is reminiscent of another Democratic senator who has turned out to be a massive disappointment to many Democrats -- Senator John Fetterman. When the voters elect loose cannons to office, sometimes they don't always get what they expect. I'm not saying Platner will also turn out to be a disappointment in a similar way, but the possibility does exist.

For now, Platner can take a breather. He won't have to spend a ton of money on primary ads any more, and he won't be attacked by a fellow Democrat for the next month. He can concentrate on defeating Susan Collins (which, to his credit, he already has been doing -- he has already been running against Collins for the most part, not against Mills). A flood of outside money backing Collins is expected for the general election, but Maine is one of those states that prides itself on being independent and looking with scorn on people from other states interfering in their elections.

Just based on the polling alone, Graham Platner had a much better chance of defeating Collins in November than Mills. He also seemed likely to win his primary even if Mills had stayed in the race. He has tapped into working-class anger in a big way and could ride that wave right into the Senate. Which is why today's development has to be seen as good news for the Democrats in general.

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant