I did not check all of them, but the pattern is that the Republican senators who voted with the democrats have just been re-elected or elected. They think they are safe from voter wrath.
The big target is Mitch McConnell, who is up for reelection in 2020. He needs to be "Cantored" to effectively send a message to the rest of them.
However, prior to that MUST be a shot across McConnell's bow, which is the upcoming reelection of Matt Bevin in 2019 as governor of Kentucky. We need to make the Bevin reelection such a huge turnout as to be a bellwether for what's ahead for McConnell in 2020.
In fact, a popular turnout for Bevin in 2019 might be a launching pad for a Bevin rematch against McConnell in 2020.
-PJ
Yes, that is true of the 12 GOP.