Mason-Dixon is out with new general election numbers in Montana (May 19-21) showing John McCain beating Obama by 8 points and Clinton by 11:

McCain 51
Clinton 40
Undecided 9

McCain 47
Obama 39
Undecided 14

The candidate's favorable/unfavorable ratings explain why Clinton runs worse than Obama:

McCain 46/35 (+11)
Obama 41/38 (+3)
Clinton 29/50 (-21)

Lastly, a bit of Montana presidential history from the Missoulan article:

In 15 presidential elections since 1948, the Democratic candidate have [sic] carried Montana only three times. Harry Truman won in 1948. Montanans backed Lyndon Johnson as part of his landslide win over Barry Goldwater in 1964. The state backed Bill Clinton over sitting President George H.W. Bush in 1992, thanks to third party candidate Ross Perot pulling in 26 percent of the vote.