Those endorsements, including one by Missouri's Claire McCaskill, show they believe the Illinois senator is electable:
After Mr. Obama’s triumph in Iowa, the names of other Senate Democrats about to take the plunge for Mr. Obama began to circulate. Then came New Hampshire, and operatives in both camps expected those endorsements might dry up as Mrs. Clinton regained her grip on the race. But they didn’t. They came anyway: John Kerry of Massachusetts, who ran with Mr. Edwards four years ago, and Tim Johnson of South Dakota. Mr. Nelson. Claire McCaskill of Missouri. Patrick J. Leahy of Vermont.
Even supporters of Mrs. Clinton say the endorsements were timely and helpful for Mr. Obama. First, they showed his New Hampshire loss had not scared people off, that influential fellow Democrats still considered him a credible rival to Mrs. Clinton. Second, the support from red and swing state lawmakers left the impression that some senators, like Mr. Conrad, believed Mr. Obama to be an easier sell than Mrs. Clinton outside Democratic strongholds.
“When you have senators from states that are not presumably blue in every election cycle support him,” Mr. Durbin said, “it at least raises the very sound argument that Barack is electable.”