Rep. Joseph Cao (R-LA) may have an interesting built-in line of defense against Republicans who would want to seek retribution over his vote for the health care bill: His overwhelmingly Democratic district.

I asked Club For Growth executive director David Keating, whose group has often supported insurgent conservatives -- Marco Rubio, Pat Toomey, Stephen Laffey and Doug Hoffman, just to name a few -- whether the group might support a primary against Cao. "Our PAC doesn't plan on backing any primary challengers to him," said Keating, "because it would be a waste of money, probably, for the general election."

Cao's district, centered around New Orleans, voted 75%-23% for Barack Obama in November 2008, by far the most Democratic district to be currently represented by a Republican. Cao won a shocking 50%-47% victory in a specially scheduled December election (due to hurricane damage) against Democratic Rep. William Jefferson, who was then under indictment and was later convicted on corruption charges.

Keating said that he doesn't know of anybody currently working on a primary challenge against Cao. He said that while such a challenge could potentially be successful among Republican primary voters, the chances would be low for the new Republican nominee to win the district in November, and that Cao would have a much stronger chance as an incumbent.

"It's not a good place for someone to get involved there, it's such a tough district for a Republican to win a general election in November," said Keating. "The circumstances that he won the race under were unusual to say the least. It's not every day that a Congressman has tens of thousands of dollars in his freezer, and to have the money seized by the government."