Washington (CNN) Ever since Susan Collins cast the deciding vote to confirm Brett Kavanaugh to the Supreme Court last October, Democrats have pledged that they will beat the long-serving Maine Republican senator in 2020.

On Monday, they took a major step in making good on that promise as Sara Gideon, the speaker of Maine's state House, announced her candidacy . "Susan Collins has been in the Senate for 22 years," Gideon says in a video announcing her candidacy. "And at one point, maybe she was different than some of the other folks in Washington, but she doesn't seem that way anymore."

In the video, Gideon hits Collins for voting for President Donald Trump's tax cuts and for Kavanaugh, and even features footage of the President thanking Collins. So you know where Gideon is headed in this campaign: Collins likes to say she's a moderate but when she's in Washington she votes like a Trump conservative.

That argument -- minus the "Trump" part -- has been tried before against Collins. In 2002 and 2008, Democrats ran serious, well-funded candidates against her. And attacked Collins as less moderate -- and less in line with Maine's values -- than she tried to paint herself. Collins won with 58% of the vote in 2002 and 61% in 2008. In 2014, Democrats barely challenged her, and she was reelected with 67%.

Collins is an able campaigner -- and she'll have as much money as she needs from Washington Republicans. (The Gideon video features Senate Majority Leader Mitch McConnell making that point.)

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