Looks like Rummy, not one to forgive and forget I guess, is McCain's latest endorsement holdout:

Former Secretary of Defense Donald Rumsfeld recently declined to answer whether he will support Sen. John McCain (R-Ariz.) for president.

McCain, the GOP presidential standard-bearer, has been one of Rumsfeld's harshest critics.

McCain has said that Rumsfeld will "go down as one of the worst secretaries of defense in history."  

The Hill talked to Rumsfeld earlier this month near his downtown D.C. office.

Rumsfeld told The Hill that he has not followed the presidential elections, but instead has been focused on work for his private foundation.

Asked whether that meant he wasn't going to support McCain, Rumsfeld answered: "I have not been involved at all."

Rumsfeld declined to comment any further. He also declined a follow-up request for comment on the issue to his personal office.

Oooh. Ouch. Not that this is really anything new for McCain, mind you. If you Google "won't endorse McCain" the results return several high profile entries including Tom Tancredo:

Rep. Tom Tancredo (R-Colo.), who has been sharply critical of McCain on immigration, told The Hill in February, "I don't like McCain. I don't like him at all."

Tancredo spokesman Mac Zimmerman said Tancredo won't endorse McCain because he fears the senator would repudiate it like he did with the formal backing of controversial pastor John Hagee.

Reps. Virgil Goode and Walter Jones:

"The Hill," a political insider guide, reports that Goode, R-5th, is among at least 14 Republican representatives who have not endorsed McCain.

U.S. Rep. Walter Jones, R-N.C., has said he can't back McCain until he has clear plans for the Iraq war, another representative has cited concerns about the candidate's various energy policies and in Goode's case, immigration is a sticking point.

Rep. Ron Paul:

Republican Rep. Ron Paul told the Tribune this morning he will not back Sen. John McCain as his party's nominee unless the Arizona senator "has a lot of change of heart."

"I can not support anybody with the foreign policy he advocates, you know, perpetual war. That is just so disturbing to me," Paul said. "I think it's un-American, un-Constitutional, immoral, and not Republican."

Senator Jeff Sessions...sort of:

Others, like Sessions, say they are supporting McCain but stop short of granting their endorsement, according to The Hill. [...]

"Senator Sessions strongly supports Senator McCain's candidacy for president. Senator Sessions has publically spoken in support of McCain and expects to continue to do that throughout the campaign."

And Senator Chuck Hagel:

Sen. Chuck Hagel, R - Neb., said this morning he is not ready to endorse Sen. John McCain, R - Ariz., for president.
Maverick Nebraska Republican not ready to endorse McCain.

"I think endorsements, at least when I endorse someone, or when I work for someone, or commit to someone, I want to be behind that person in every way I can," Hagel said in an exclusive "This Week" interview.

Hagel pointed to their differing views over foreign policy in explaining his hesitation. "I've obviously got some differences with John on the Iraq war. That's no secret.

Umm, so, who's the candidate who's having trouble uniting his party again?