In his Evans-Novak Political Report, Robert Novak - who has the pulse of the Conservative movement - examines potential problems for McCain. Novak (and co-writer Tim Carney) see problems for McCain with libertarian and evangelical factions of the conservative movement:

1. Rep. Ron Paul (R-Tex.), who garnered significant chunks of the Republican primary electorate in the late primaries, has made it clear he will not endorse McCain. Paul’s loud and enthusiastic following is small, but if they stay at home or vote third-party in tight states, they could help Obama. McCain will have trouble appealing to limited-government conservatives, but when contrasted with Obama, he could win back many of the Paul followers.
2. The key question on the libertarian side of the ledger will be the strength of former Georgia Rep. Bob Barr, the Libertarian nominee. Barr lacks the rock-star quality of Paul, and his mixed record on foreign policy, domestic security, and gay marriage will turn off some of the libertarian purists. Will he appeal to disaffected small-government conservatives?
3. Barr sees his strongest region being the Mountain West, where Nevada and Colorado sit on the edge of the McCain-Obama battle. Barr could tip those states in Obama’s direction if he gets just 2 percent.
4. The fear of Barr swinging his home state Georgia to the Obama column is overblown. Bush won 58% in Georgia in 2004, and a higher black turnout in 2008 would be partially offset by the white Democrats who vote Republican. Also, remember that Barr lost a GOP primary to end his congressional career, so he is hardly Georgia’s favorite son.
5. On the religious conservative side, McCain is also facing difficulties. Ineptitude and insensitivity resulted in insults to two evangelical leaders, the Rev. John Hagee and Focus on the Family’s James Dobson.
6. Hagee has told friends that McCain “threw [him] under the bus,” by soliciting his endorsement, and then disowning him after news came out about a previous offensive-sounding comment about Hitler (Hagee actually has very strong ties to the Jewish community, but many groups objected angrily to the comments). McCain’s rush to disavow Hagee while Hagee was searching for a more gracious exit route shows the nominee’s clumsiness.
7. McCain also bungled an opportunity to patch things up with Dobson, who is very influential. Dobson had said last year that he could never vote for McCain, but this spring, he reached out to the nominee. Dobson wanted a meeting in Colorado Springs, but McCain demanded a meeting in Denver. No meeting ever happened.
8. There is little in McCain’s record as a senator to upset evangelicals, but little to excite them either: He opposes gay marriage, but voted against the Federal Marriage Amendment; he votes pro-life on most issues, but he is hardly vocal about it. To evangelicals, however, he doesn’t come across as “one of us.” These missteps can emphasize that problem, depressing turnout in a constituency that has been a core of GOP presidential victories starting with Ronald Reagan.
9. Add to this McCain’s un-conservative tastes, as exemplified by the two men he would most like to name as his running mate: former Homeland Security Secretary Tom Ridge and Sen. Joe Lieberman (ID-Conn.). Either of these VP nominees would destroy his conservative support, and McCain surely knows that.