It’s too bad in a way. Conventions used to give voters an easy way to look at how the parties were presenting themselves. Now, the sole big media events that matter are the debates.

There has been a push-pull effect on convention coverage: As they became more highly produced party commercials, the conventions became less and less attractive to viewers. And the more viewers went off in search of broadcast alternatives, the more reluctant the traditional networks became to pull their popular shows for an entire evening. I really dislike the idea of politics becoming a niche product. That’s not very democratic -- and note the small “d.” But I don’t see what will reverse the Great Shrinking of the Conventions.

The Isaac Effect, however, goes well beyond the disruption it has caused to the Republicans’ schedule. For perfectly good reasons, media organizations are transferring people toward New Orleans. And the anniversary of Katrina inevitably politicizes the story. It is inevitable that President Obama’s handling of this storm and its aftermath will be compared with George W. Bush’s handling of Katrina.

On its face, this is good news for Democrats: Any reminder of Bush’s response to Katrina recalls the aspects of the Bush years voters would prefer to forget. These are the failures that helped Obama win four years ago.

Still, the pressure on Obama to perform well if this storm hits New Orleans — and everyone still hopes it doesn’t — will be enormous. In the extraordinarily partisan pre-election environment, the administration’s every failure or shortcoming will be magnified by the GOP. Every crisis is an opportunity for an incumbent, and in such crises lurk great dangers.

Thus: Isaac, its impact and the administration’s handling of the storm’s effects all seem likely to loom larger this week than Mitt Romney’s big moment. If Romney breaks through despite this, it will be the mark of an extraordinary performance.

This was already a peculiar campaign. Defining and measuring the Isaac Effect will be another strange phenomenon that will keep political scientists busy long after the election is over.

— Updated with minor editing, 7:01 p.m.