Santorum's departure Tuesday has pushed former Massachusetts Gov. Mitt Romney closer to the nomination. But Gingrich and Paul say there is still time left for voters to pick a more suitable alternative to face President Barack Obama in November.
Paul's campaign says he is "the last—and real—conservative alternative" to Romney.
Gingrich took to Twitter to call Santorum's departure "the last stand for conservatives" and to urge supporters to donate to his campaign.
Money is an issue for Gingrich. Utah officials say his campaign's $500 check to get on the ballot for Utah's primary has bounced. His campaign says a new check will be issued.