Rep. Bill Cassidy defeated three-term Democratic Sen. Mary Landrieu in Louisiana's Senate runoff election Saturday night, stretching the GOP's 2014 gains to nine seats and giving the party 54 senators starting next year.
The Associated Press called the race quickly.
Landrieu had finished first in the all-party primary a month ago but got only 42 percent of the vote, while the second-placed Cassidy and fellow Republican Rob Maness combined for a majority of the votes cast in November. Maness endorsed Cassidy for the runoff.
Landrieu's campaign poured most of its resources into that initial primary, hoping to win an outright majority victory while Republicans' votes were still divided and thus avoid a runoff. But after a weak showing in November and certainty of a Republican takeover of the Senate, fellow Democrats largely left Landrieu to fend for herself in the runoff.
The Democratic Senatorial Campaign Committee canceled its reserved TV advertising time for the runoff, while many of the most monied Democratic groups, such as environmental PACs and the pro-abortion-rights EMILY's List, steered clear of the race because of Landrieu's stances on energy policy and abortion.
Cassidy, a physician and former state legislator, has been promised a position on the Senate's powerful Energy Committee that Landrieu now chairs. Landrieu argued during the campaign that the chairmanship gave her the clout to deliver for Louisiana oil and gas interests. But voters focused more on Landrieu's vote for Obamacare and support for other Democratic policies.