The Wall Street Journal:

President Barack Obama's endorsement of gay marriage has put a new wrinkle in the Democrats' battle to retain control of the Senate, with many of the party's candidates in conservative states keeping their distance from the president on the hot-button issue.

Sen. Jon Tester in Montana, Sen. Claire McCaskill in Missouri and former Gov. Tim Kaine in Virginia have declined to support same-sex marriage, even as Mr. Obama's backing has galvanized the party's liberal wing and activist ranks.

Even senators facing less-competitive races—Bob Casey of Pennsylvania, Joe Manchin of West Virginia and Bill Nelson of Florida—have sought distance from Mr. Obama on same-sex marriage.

... Republicans need to pick up four seats to capture a majority in the Senate, now controlled by Democrats by a 53-47 margin.