From Chuck Todd:

There’s plenty of evidence to suggest that President Bush may have been the deciding factor that killed the GOP’s momentum in some key Senate races over the last week. One Republican consultant is convinced that Bush’s last-minute visit to Missouri on behalf of ousted GOP Sen. Jim Talent did the incumbent in. According to the network exit polls, Democrat Claire McCaskill crushed Talent among those late-breaking voters who decided in the final three days (a full 11 percent of the electorate). Bush also made a last-minute trip to Montana, where anecdotal evidence indicates the president’s rally for Republican Conrad Burns stopped the incumbent’s momentum in Billings.