U.S. Republican presidential candidate Newt Gingrich has notified his supporters that he is dropping out of the race, a day before he makes his official announcement.

Gingrich posted a video on his website Tuesday thanking the nearly 180,000 people who donated to his campaign and the nearly 2.5 million who voted for him in the Republican nominating contests.

Without mentioning Mitt Romney, the presumed Republican nominee, Gingrich said the country is still faced with a “tremendous crisis” and said re-election of Democratic President Barack Obama would be a “genuine disaster.”

Gingrich won two primaries during this campaign: his home state of Georgia and its neighbor South Carolina. He had fallen far behind Romney and Rick Santorum in opinion polls, staying ahead only of libertarian candidate Ron Paul.

Gingrich's spokesman hinted last week that Gingrich would leave the race after Romney swept all five states that held primaries on April 24.

Santorum dropped out of the race last month. Paul is still in the running, although he has no chance of winning enough delegates to be the party nominee in the November presidential election.