Addressing cheering supporters in California before polls here closed, Biden said, “It’s still early, but things are looking awful, awful good.”

For anyone who predicted the race might be over by Super Tuesday, he said, “Well, it may be over for the other guy."

It is far from over, of course. Sanders was immediately declared the winner in California. But Texas marked a significant defeat for Sanders. He had been leading in recent polls, and many observers predicted early votes cast in that state would preserve a victory for him there. Instead, Biden surpassed him.

Sanders, speaking at his rally in Burlington, Vt., on Tuesday night, predicted the night would end well for him despite Biden's string of wins. "We're doing well in Texas right now, we won Colorado, and I'm cautiously optimistic that later in the evening, we can win the largest state in this country, the state of California," Sanders said to cheers.

The early results appeared likely to narrow the race to Sanders and Biden, with the rest of the field barely hanging on. Biden won Elizabeth Warren's home state, Massachusetts, and Mike Bloomberg was teetering elsewhere. After skipping the first four nominating states but spending hundreds of millions on TV ads, Bloomberg received disappointing news in the quick calls for Biden in Virginia and North Carolina. He did, however, win American Samoa.

Most likely, the set of elections, in which about one-third of delegates will be awarded, will culminate in a grouping of Democratic voters around opposite poles — progressives to Sanders and moderates to Biden.

Sanders, after wins in New Hampshire and Nevada, raised nearly $47 million in February alone, when he became the frontrunner in the contest and saw his rival progressive, Warren, fall far back. Sanders has been drawing crowds of thousands to rallies in California and Virginia in the run-up to Super Tuesday.

Sanders' win in California was especially significant. It is the largest delegate haul by far and a state he failed to carry in his unsuccessful 2016 run. But because of late balloting, the results from California could take days or weeks to count — and even small margins in that state could be significant to Biden, Bloomberg and Warren.