When Michael Cohen showed up at Novartis AG last year proposing to help the drugmaker navigate the Donald Trump administration, it sounded like a promising opportunity. Cohen had, after all, served as an attorney for Trump and had close ties to the new president.

It didn¡¯t take long for Novartis to conclude Cohen was full of hot air. And soon ¡ª but not soon enough ¡ª the company realized he was also a hot potato.

After the first meeting between Novartis officials and Cohen, in March 2017, ¡°it was clear that he had oversold his abilities,¡± said Joe Jimenez, the company¡¯s chief executive at the time.