Charles Krauthammer said on "Tucker Carlson Tonight" that it's reasonable for Special Counsel Robert Mueller to look into Russia-connected business deals by the Trump family.

Krauthammer reacted to the new report that Mueller's probe has expanded to examine a range of business transactions by the president and his associates.

President Trump told the New York Times just one day before that looking at his family's finances would be outside the scope of the probe.

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Krauthammer said there is little Trump can do about Mueller's probe because the former FBI director is "politically unfireable" and has a broad mandate from the Justice Department to look into potential collusion between the Trump campaign and Russia.

"Trump would be engulfed if he tried to [fire Mueller]," he said, noting that legally, Trump could take the controversial step.

Krauthammer noted that going beyond Russian business deals would then be a "fishing expedition" by Mueller.

"It is reasonable to follow the money," said Krauthammer, adding that Trump seemed to indicate there was a "red line" if Mueller goes beyond Russia-linked deals.

Watch his full analysis above.

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