But for the Reps that are in purple areas, it might be. Being seen to support the Felon could be dicey in those areas, don't you think?

Nope. People hate a turncoat more than an enemy. It doesn't matter whether your state is purple or not - you can't win re-election unless you win your primary, and your primary is going to be all (or nearly all) Republicans. And even in a purple state, a lot of those Republicans are not going to be happy that you voted against your own party's leader.

If you needed only one or two Republican Senators, maybe you can find them. There's always someone retiring, or someone who feels strong enough to win their primary. But twelve? Name the twelve Republican Senators whose states are so purple that they would rationally decide that vote in favor of impeachment was in their own political interest, rather than a guaranteed ticket to destroying their political career.