On Wednesday evening, as the senators gathered to vote on the $700 billion financial rescue package, Mr. Obama, Democrat of Illinois, walked over to the Republican side of the chamber to extend a greeting to Senator John McCain of Arizona.
While it took Mr. Obama several seconds to make his way over to Mr. McCain, the actual handshake lasted barely a second, as Mr. McCain responded with a chilly look, a turn of his head and a brief return handshake.