He may have clinched the nomination a long time ago, but people continue to vote against him in surprisingly large numbers:
I’ll cop to forgetting, completely, that Idaho held its primaries yesterday, and I missed watching Ron Paul score 24 percent of the vote. (John McCain got 70 percent, with the rest going to some guy named Uncommitted, who’s pissed that Hillary Clinton is trying to steal his Michigan delegates.) That was a disappointing result for some Paul backers, who thought the congressman might actually win the primary given the rock-bottom GOP enthusiasm and Paul’s strength in northwest Idaho.
Well, 24% isn’t bad either, and seems to be an indication of a certain number of Republicans who really don’t like their nominee.
Also, in case you’re wondering why Ron Paul doesn’t appear ready to endorse Bob Barr, here’s one explanation:
[H]e’s neither going to endorse Bob Barr nor the Constitution Party candidate—maybe not even after the Republican convention wraps up. At issue is Paul’s congressional seniority. He’s worried, and rightfully so, about losing his precious banking committee seat if he hands over too much support to third party candidates who are trying to bleed the GOP.
Something tells me that the GOP is going to be so shell-shocked come November, they won’t be thinking much about Ron Paul.

[...] as I noted earlier this week, Reason’s David Weigel reports that endorsing a third-party candidate would hurt Paul’s [...]