Political leaders have shunned the Alternative for Germany. But on his social media platform X, Mr. Musk is pitching the party as mainstream.

The publicity was a potential boon for AfD, which has been frozen out of mainstream politics, in part, because its leaders have downplayed Nazi atrocities.

Elon Musk praised the co-leader of the German party Alternative for Germany (AfD) as “very reasonable” on Thursday, urging Germans to vote for the far-right party in what is the latest high-profile sign of the tech billionaire’s involvement in European politics.