It's a little more complicated. The Supreme Court has already ruled that Trump can fire agency heads not for cause even when there is a "for cause" clause in the law. The Court then invented a new "the Federal Reserve is special" clause that prevents Trump from using that exact same power on Fed Governors. So because the Court has made a patchwork quilt out of the law (in an effort to bring about their preferred policy outcomes), Trump is now trying to muster "cause" against Cook. Early signs indicate that the case appears to have serious problems.

"For cause" does not and has never meant "due to actions before and outside of the scope of their work."

The Russian playbook.

Just wait until opposition candidates start getting disqualified for an unpaid parking ticket (while the incumbent had his fingers in a tank assault on the Duma, or three different election fraud conspiracies and one failed coup).