Wall Street's major indexes closed sharply lower on Monday, after U.S. President Donald Trump announced hefty tariffs against Japan, South Korea and other trading partners while Tesla shares sank after CEO Elon Musk said he was forming a new U.

Stock shares in Elon Musk's car company Tesla fell about 7% Monday after the billionaire ex-DOGE chief announced plans to form his new "America Party."

Mr. Musk’s involvement in politics and his financial support for the president’s campaign was once seen by investors as a benefit to Tesla, fueling a steep rise in company shares after the election last year. That association has now turned into a liability. Tesla shares are down 40 percent from their peak in December.