Black, Democratic, liberal and younger voters were generally for the deal, while white, Republican, conservative and older voters were more likely to be opposed. In fact, you can explain 82 percent of the variation in support for the Iran deal in 18 subgroups just by knowing what Obama’s job approval rating was in each group.

The matchup isn’t perfect. There are, for example, plenty of Republicans (34 percent) in favor of the deal and plenty of black people (31 percent) against it. But it wouldn’t be surprising if those groups returned to the partisan fold as the debate reaches a climax.

The partisanship on display in this issue was also apparent during the gun control debate after the Newtown school massacre in Connecticut. You probably remember how the initial polling seemed to show that there was a lot of support for Obama’s proposals. But once Obama’s name was attached to the legislation, support for any bill lined up almost perfectly with how people felt about members of his administration.