By James Oliphant and Luciana Lopez

MIAMI, March 9 (Reuters) – Democratic presidential candidate Bernie Sanders boasted at a debate in Miami on Wednesday that his upset win in Michigan’s primary the day before over front-runner Hillary Clinton had rejuvenated his campaign and strengthened his case for being the party’s nominee.

Sanders pointed out that some observers consider the victory, which was not forecast by opinion polls, “one of the major political upsets in modern American history.”

The senator from Vermont said the task before him was to convince the so-called Democratic “superdelegates,” party elites who have largely sided with Clinton, that he “is the strongest candidate to defeat (Republican front-runner) Donald Trump,” Sanders said.

Asked about the Michigan loss, Clinton said. “It was a close race. I’ve won some. I’ve lost some.”

Both Democrats harshly criticized Trump, with Clinton accusing him of “trafficking in paranoia.”

“I think the American people are never going to elect a president who insults Mexicans, who insults Muslims, who insults women, who insults African-Americans,” Sanders said.

Earlier on Wednesday, Republican leaders opposed to Trump becoming the party’s U.S. presidential candidate in the November election warned that the billionaire businessman could become unstoppable if he wins two crucial nominating contests next week.