It’s not just the seven Democratic Senate seats in red states Mitt Romney carried that are in danger because of ObamaCare. In 2010, four of the six Senate seats Republicans picked up were in states carried by Mr. Obama in 2008. Mr. Obama will be less popular in such purple states in 2014 than he was last November—and so will Democrats who have been passive, reliable votes for him.

So Democratic senators in purple states, like New Hampshire’s Jeanne Shaheen, are at risk for having declared, as she did, “One of the things that I said as a requirement that I have for supporting a bill is that if you have health coverage that you like you should be able to keep that.” Colorado Sen. Mark Udall will get intense blowback for mimicking Mr. Obama’s pledge, “If you like your current plan, you can keep it.” And Virginia Sen. Mark Warner can’t escape having pledged: “I’m not going to support a health-care reform plan that’s going to take away the health care you’ve got right now.”

ObamaCare will also hurt Democratic congressmen attempting to become senators. Examples are Iowa’s Bruce Braley, who asserted that ObamaCare would “allow Americans to maintain their choice of health insurance” and Michigan’s Gary Peters, who said “If you’re covered and you like your insurance, you can keep it.”