Charles Krauthammer reacted to the Washington Post report that Special Counsel Robert Mueller expanded his investigation to include possible obstruction of justice by President Trump.
Mueller was originally named to investigate claims of collusion between Trump and the Russians.
However, in the wake of ex-FBI Director James Comey's firing, questions were raised about Trump's conduct in meetings with him.
Krauthammer called it a "classic case of a special counsel expanding the scope of his investigation."
"The metastasis has begun," he said.
Krauthammer said Mueller is now the "most powerful man in Washington."
He pointed out that although Trump can legally have Mueller fired, it would likely be politically devastating to him.
Watch the clip above.