I get why Democrats don't like Susan Collins, but the outrage is exaggerated. She's like the only Republican Senator from a blue state, right? (Okay, if we count Gardner, there's 2). And it's not as if Maine is solidly Democratic anyway. However, there's five Democratic Senators in states Trump won by at least 15 points and they're all way to the left of their states (with the exception of Manchin). I've never seen Democrats call them "fake moderates". This is a Republican problem, not really a Democratic one.
If you want Republican policies, you should vote for a Republican candidate for Congress, no matter how hard the Democratic candidate tries to be a " nice guy moderate FF who will clean up the mess in Washington ". Same is true for other side as well, of course. Atlas generally understands this (okay, most of Atlas does), but the typical American "swing" voter does not. I'll never understand how a Republican can vote for Heidi Heitkamp for Senate or how a Democrat can vote for Susan Collins. This is just dumb.
Solid Rs/Ds don't vote against their party. But even in states like North Dakota and Maine, there are a lot of registered independents, plus people who are only registered with a party for reasons related to the primary season. Sure, they may vote one way or the other 80% of the time, but they don't mind the occasional Susan Collins or Heidi Heitkamp, both of whom are moderates by any reasonable standard.