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

Musk tested the boundaries of foreign election interference, hosting AfD co-leader Alice Weidel for a livestream interview on X.

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.