WASHINGTON, Mar. 5 (Xinhua) - U.S. President Joe Biden and former President Donald Trump are leading in "Super Tuesday" wins in their respective party's primaries of the 2024 presidential election.

Biden, challenged by American author Marianne Williamson and Congressman Dean Phillips, has won Alabama's, Massachusetts's, Maine's, North Carolina's, Oklahoma's, Tennessee's, Virginia's, and Vermont's Democratic primaries and the party's caucus in Iowa, according to U.S. media projections.

Trump, meanwhile, has been projected to pick up victories in the Republican primary contests in Alabama, North Carolina, Oklahoma, Tennessee, and Virginia, beating former South Carolina Governor and former U.S. Ambassador to the United Nations Nikki Haley.

Projected results continue to roll in on the night of "Super Tuesday," the biggest day for the primary race of the 2024 U.S. presidential election.

Fifteen states, including populous California and Texas, and the U.S. territory of American Samoa, held primary elections on Tuesday. Iowa Democrats released the results of their presidential caucus earlier this day.

A recent survey by The Associated Press-NORC Center for Public Affairs Research found that a significant share of U.S. adults doubt the mental capabilities of Biden, 81, and Trump, 77, in what could be a rematch of the 2020 election.

More than six in 10 say they are not very or not at all confident in Biden's mental capability to serve effectively as president, while 57 percent say that Trump lacks the memory and acuity for the job, the poll showed. About four in five American adults think the United States is headed in the wrong direction while one in five think it is going the right way.