Since news broke Tuesday of Senator John McCain’s (R-AZ) diagnosis of brain cancer, outpourings of support have come from both sides of the aisle calling the decorated Navy veteran a tough fighter who will not go down easy.

They were not kidding.

As he recovered from surgery and prepared for new treatments at his Arizona home today, the six-term Senator found the energy to encourage his Twitter followers to read Michael Gerson’s Washington Post column, entitled “Trump’s breathtaking surrender to Russia.”

There is nothing subtle about McCain’s move against the president. Gerson writes of the tremendous “cost of Trump’s Russophilia” and argues that the president’s actions are “effective permission for a broad, unconventional Russian offensive, designed to…restore lost glory at the expense of neighbors and American interests.”

“If this is what Trump’s version of ‘winning’ looks like,” Gerson asks, “what might further victory entail? The recreation of the Warsaw Pact? The reversion of Alaska to Russian control?”

McCain attack on Trump — and at a time when both parties and the media are paying homage to his service — may be the first sign of a true divide in the Republican Party.

Whether or not, Congress will react with the political courage to hold Trump accountable remains to be seen. But if McCain is looking to reclaim his maverick mantle, this is a bold and much-needed start.