Recent polling finds that Democrats Russ Feingold (Wisconsin), Evan Bayh (Indiana), and Michael Bennet (Colorado) are all doing quite well in their respective Senate races versus Republicans Ron Johnson, Todd Young, and Darryl Glenn. But essentially all of that polling was done before Aetna announced that it is bailing out of most of the Obamacare exchanges, thereby speeding up Obamacare's slow-motion death spiral.

Alone among those running in competitive Senate races this time around, Feingold, Bayh, and Bennet actually voted for Obamacare. Indeed, without each of their votes—which gave Democrats the necessary 60 votes in the Senate—we wouldn't have Obamacare. That should be a potent message to voters.

In 2010, Feingold actually lost his seat to Johnson by almost 5 percentage points in the wake of his Obamacare vote. Bayh retired that year rather than face Indiana's voters. And Bennet survived the 2010 election by less than 2 points largely because he ran against Ken Buck, who let Bennet off the hook on Obamacare and whose peculiar campaign philosophy was that ads critical of the other candidate are wrong.

It will be interesting to see whether Johnson, Young, and Glenn will focus on making their races referendums on the centerpiece legislation of the Obama presidency. (They could also make them choices between Obamacare and the House GOP Obamacare alternative.) Running nonstop ads focused on their opponents' Obamacare votes, and on their opponents' praising of the 2,400-page disaster that they helped spawn at the American people's expense, could well enable these underdogs to erase their current deficits.

For there is no issue that quite tells the ugly story of big government, profligate spending, and elite hubris like Obamacare. There's a reason why, during Obama's second term, a whopping 98 percent of polls, according to RealClearPolitics, have found Obamacare to be unpopular. But only in Wisconsin, Indiana, and Colorado do voters have a real opportunity to punish those who are directly responsible.