One well-connected GOP insider said Ryan’s budget is “our version of cap-and-trade.”

The source, who requested anonymity, added that Republican “rank-and-file members are very, very concerned that this was the canary in the coalmine on Medicare and it’s going to affect all of the other difficult votes that leadership is going to ask them to make.”

All but four House GOP lawmakers supported Ryan’s budget blueprint two months ago. Since then, Democrats have seized on that vote, repeatedly claiming that Ryan’s measure would “end Medicare as we know it.” Political analysts contend Medicare played a major role in New York Democrat Kathy Hochul’s upset win in a special election to replace former Rep. Chris Lee (R) on May 24.