Here's a good case study in how people get trapped in conventional wisdom that's wrong. I speak of Ohio GOP Senator Rob Portman, showcased at TPM this morning because he misled a voter about his position on background checks--like Kelley Ayotte and Jeff Flake, trying to make it sound like he backed them even after he voted against them.

Portman, you'll recall, announced his support for same-sex marriage back in mid-March. Then a poll came out in April showing that he lost a lot of ground among Republicans, going from just 8 percent disapproval to 21 percent. He also gained among Democrats. But what good does that do him?

So he figured well, I went left on gays, but I can't do it on guns, too. That's too much for the voters of Ohio. Right?

Wrong! He dropped in the polls after his gun vote too! Here's the PPP analysis from late April:

Portman's approval has dropped a net 18 points over the last 6 months from +10 (35/25) in October to now -8 (26/34) in April. Portman's popularity decline has come across the board with Democrats (from 15/39 to 8/50), Republicans (62/11 to 46/19), and independents (28/23 to 24/32) alike.

72% of Ohio voters support background checks, including 87% of Democrats, 73% of independents, and 56% of Republicans. 36% of voters in the state say they're less likely to support Portman in a future election because of this vote to only 19% who consider it to be a reason to support him.

Seems pretty clear: His background-check vote hurt him, probably across the board. So he screwed up twice. Except of course than on marriage equality he was right on the merits.

The gun question is going to come up again. There are lots of potential vote switches from nay to yea. They just have to not be reflexive and chickenshit, and they have to go out around their states and explain the bill and their votes. The problem is that lots of senators don't want to do that. It's work.

On the Democratic side, Mark Pryor is the best example of the problem. He knows the NRA will never endorse him against a Republican. But in voting against background checks, he is clearly hoping that he can prevent the group from spending $2 or $3 million against him. But of course they might do that anyway. So why not shore up your base and show some guts? Because all elected officials want, in the first instance, the path of least resistance to reelection. That's what Portman thought: If I do the gun thing after the gay thing, I'm gonna have too much explaining to do. But now, as today's TPM item shows, it's just the opposite!