Tesla shares fell nearly 8% on Monday after CEO Elon Musk's plans to launch a new U.S. political party reignited concerns about his commitment to the company's future as it struggles with declining sales.

Mr. Musk’s involvement in politics and his financial support for the president’s campaign were 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.

Tesla stock price fell Monday after Musk said he's formed the America Party, the latest development in the billionaire's feud with President Trump.

The Tesla CEO says both parties have failed and claims The American Party will fight government bloat, attract disillusioned Democrats, and shake up the system.

Elon Musk isn't done with politics just yet. Days after the SpaceX and Tesla CEO threatened to form his own political party as an alternative to America's "Democrat-Republican uniparty," Musk has announced his pledge to do so.