Bernie Sanders vowed Wednesday to push forward in the 2020 presidential race despite the latest series of blows to his White House ambitions, including campaign challenges posed by the coronavirus pandemic.

The Vermont senator admitted that Tuesday "was not a good night for our campaign from a delegate point of view." Even so, he said he would stay in the race at least through Sunday's debate with former Vice President Joe Biden.

"Donald Trump must be defeated, and I will do everything in my power to make that happen. On Sunday night, in the first one-on-one debate of this campaign, the American people will have the opportunity to see which candidate is best positioned to accomplish that goal," Sanders told reporters at his Vermont headquarters. He spoke in Burlington on Wednesday for the first time since another round of Democratic primaries squeezed his hopes of winning the party's presidential nomination.

Results from "Big Tuesday" all but quashed the Vermont senator's push to rack up a majority of pledged delegates. Carried by projected wins in Mississippi, Missouri, Idaho and all important Michigan, Biden took a decisive step toward facing Trump in November. Sanders will win North Dakota's caucus, while Washington state's primary is still too close to call, according to NBC News projections.

The coronavirus outbreak has also hampered Sanders' efforts to keep pace with Biden. The senator, who relies on jammed indoor events to muster support more than his rival does, had to cancel a Cleveland rally Tuesday because of the crisis. Biden also canceled a primary night event in Cleveland and addressed a smaller group of supporters in Philadelphia for his victory speech.

Sanders, the race's front-runner a mere two weeks ago, now needs a rapid turnaround — the likes of which Biden saw when his campaign floundered ahead of the South Carolina primary on Feb. 29. The coming days may offer his last chance to alter the race.