In a little-noted exchange Wednesday, House Speaker John Boehner, R-Ohio, who has been careful not to take sides in the Republican presidential primary, was asked by Politico's Mike Allen about Newt Gingrich.

"I'm not sure he's as conservative as some people think he is," Boehner responded.

Boehner has a long, tortured history with Gingrich (like many Republicans who have been around since the 90s), but his response is the latest indication that Gingrich has a big problem that goes beyond his personal life or his infamous lack of discipline or his "zany" ideas: Many conservatives just don't trust him.

Consider:

• National Review, the conservative magazine founded by William F. Buckley, published a scathing editorial Wednesday against Gingrich because of his "impulsiveness, his grandiosity, his weakness for half-baked (and not conservative) ideas";

• Radio host Glenn Beck has been ranting against Gingrich for days, suggesting that he is no better than Obama (and, get this, Beck suggested that the only reason somebody would vote for Gingrich over Obama is race);

• Gingrich has virtually no support from the leading Republicans in Congress and some of them are on a crusade to stop him (witness Sen. Tom Coburn of Oklahoma, another Republican with a tortured history with Gingrich, who has suggested Gingrich is unfit to be president);

• Right-wing, radio-show host Michael Savage, in a publicity stunt, offered Gingrich $1 million to drop out of the race.

And there's more.

My point: As Gingrich is relentlessly attacked in the coming days and weeks, the most devastating line of attack in a Republican primary might be that he is insufficiently conservative and that GOP primary voters might want a conservative alternative to Romney, but the guy who sat down on a couch with House Minority Leader Nancy Pelosi, D-Calif., and wants to see FDR on Mount Rushmore is not the one.

As for Boehner, he did add that although Gingrich is not as conservative as most people think, he is a conservative.  Then asked whether Gingrich would be a good president, Boehner ducked the question.