The loss of Pennsylvania, as projected by MSNBC, is a significant blow to Sen. John McCain (R-Ariz.), but it does not nearly put him out of the race.

However, McCain is in a position now where he can ill afford to lose almost any of the midsize battleground states like North Carolina, Indiana, Virginia or Missouri, where polls are close but which were rated too close to call as this was filed. McCain was projected by CBS News to win in West Virginia, a state that if he lost could have signaled an early end to the evening. Sen. Barack Obama (D-Ill.) will be in an almost impregnable position if he takes big battleground states like Ohio or Florida, which are tossups, or Georgia, where McCain has been slightly ahead.

With Pennsylvania apparently out of his column, the pressure is also greater for McCain to win in hotly contested Western states like Nevada, Colorado and New Mexico, where polls show Obama slightly ahead. If Obama is able to pick off McCain’s home state of Arizona, with its 10 electoral votes, he will also be hard to beat. McCain is ahead in the state but is having a surprisingly tough time defending it, according to recent polls.

Hotly contested states where polls close at 9 p.m. include Arizona, New Mexico and Colorado, as well as in Minnesota, where one recent poll showed a close race but others have pointed to a sizable Obama lead.