Washington, March 11 (RHC)— Former Vice President Joe Biden won four of the six states that held primaries on Tuesday to define the Democratic presidential candidate in the United States,  dealing a hard blow to the aspirations of Vermont Senator Bernie Sanders.

The states holding primaries were Idaho, Michigan, Mississippi, Montana, North Dakota, and Washington. Sanders won in North Dakota and Washington.  He lost the four others, including Michigan, the biggest prize that he won in 2016.

The loss in Michigan is a significant blow that diminishes Sanders' chances of victory, according to analysts.

Biden's outright victory once again underscored his strength among the working class and African Americans, groups vital to winning the Democratic nomination.

Joe Biden now looks set to extend his lead in the delegate count ahead of Sunday's debate in Phoenix, and the primaries in Arizona, Florida, Illinois, and Ohio set for next Tuesday.

Seemingly acknowledging that he was on course to win the nomination, Biden thanked Sanders supporters for their "tireless energy and their passion."

Having accompanied President Barack Obama for eight years in the White House seems to have played into Biden's hands among African-American voters against Sanders.

The senator from Vermont now lags even further behind in the race to become the Democratic Party's candidate in the November election, but still shows no sign of quitting his campaign.

Sanders complained over the weekend that the party's elite turned against him and in favor of Biden after several exasperated presidential candidates publicly announced their support for the vice president.