President Biden is facing an unexpected contender ahead of Super Tuesday this week — the "uncommitted" vote.

Why it matters: The movement is building momentum after over 100,000 Michigan Democratic primary voters cast ballots for "uncommitted" in protest of the Biden administration's support for Israel's government in its war with Hamas.

• Arab American and Muslim voters upset with Biden's handling of the war are hoping to send him a message at the polls, as they did in Michigan where the same voters were key to his 2020 win in the swing state.

Zoom out: Now, there is a wider push for primary voters to follow suit and cast ballots for "uncommitted" instead of Biden on Tuesday when 15 states and one territory vote in primaries.

• At least half of those states have an "uncommitted" line, no preference option or write-in slot on their Democratic presidential primary ballot, including Massachusetts, Minnesota, Colorado, North Carolina, Tennessee, Vermont and Alabama.

Zoom in: The Democratic Socialists of America, which has more than 92,000 members and chapters in all 50 states, announced Sunday it's endorsing the movement, along with its local chapters.

• The Colorado Palestine Coalition also said they were organizing a campaign to vote "noncommitted" in the state's Tuesday primary.
• Ahead of the Minnesota primary, seven Democratic-Farmer-Labor (DFL) Party legislators endorsed the "uncommitted" campaign.

Between the lines: Democratic lawmakers publicly and privately cautioned that the sizable anti-Israel protest vote in Michigan's primary was a warning sign for their party ahead of the November elections.

• Staunch Biden allies and Israel supporters focused on the fact that the 13% "uncommitted" vote was roughly in line with what former President Obama saw in his uncontested Michigan primary in 2012, Axios' Andrew Solender writes.

What they're saying: "That message has been received," Biden campaign co-chair Mitch Landrieu told NPR last week.

Go deeper: Michigan's "uncommitted" vote sounds alarm for Biden