Rogers welcomed Stevens' endorsement and said it showed "courage" during brief remarks with reporters outside the church.

Many of Stevens' staff reportedly resigned immediately after her announcement, while the chair of the Democratic Party in Michigan said her decision "shows that she has abandoned everything she claims to care about".

"We reject the attempts by Stevens and bad-faith actors to divide our party and undermine our momentum," Curtis Hertel said in a statement.

Over the weekend, as Stevens' criticism of El-Sayed escalated, a number of Democratic politicians in Michigan publicly encouraged her to end the feud and back the party's candidates more directly.

"I have no idea what the hell Haley Stevens is doing," State Senator Mallory McMorrow told CNN.

On Sunday, Democratic Senator Chuck Schumer said he and the party were firmly behind El-Sayed, without mentioning Stevens by name.

"Senate Democrats are united in our support for Abdul El-Sayed, because we know he will fight for the economic interests of working families in Michigan," he said.

After a bruising and sometimes bitter campaign earlier this year, El-Sayed, a left-wing outsider, defeated Stevens, the establishment-backed congresswoman, to win the party's nomination for the US Senate race.

The primary, and the pair's subsequent feud, has underlined divisions over the party's direction of travel ahead of the 2028 presidential election.

Former public health official El-Sayed, who is the son of Egyptian immigrants, has channelled grassroots frustration with Washington politics as well as US ties to Israel.

Stevens is a more centrist Democrat - and had the support of party figures such as Michigan Governor Gretchen Whitmer during the primary.