Jay Parini, a poet and novelist, teaches at Middlebury College. His most recent novel is "The Damascus Road," a novel about Saint Paul. The views expressed in this commentary belong to the author. View more opinions at CNN.

(CNN) We've recently learned two things about Bernie Sanders: that he had a heart attack, and that he was not immediately forthcoming with the news. I wouldn't go so far to call this a "cover-up," not in the Age of Trump, where an entire presidency is a cover-up. But it's dismaying, as it feels like political "business as usual" for Bernie to lack transparency, even for a few days, and even under these vulnerable conditions.

Jay Parini

Bernie is my senator, a fellow Vermonter. (Like most people around here, I call him Bernie.) I've been a supporter since he ran for mayor in Burlington some 30 years ago. In my view, no American politician has done more to advance progressive causes in the United States, pushing the Democrats from terrified middle-of-the-road positions on health care and economic inequality to a place we never dreamed we'd see in this lifetime.

He has spoken loudly for the poor, the disenfranchised. He was an early opponent of the Iraq War, unlike Joe Biden. He has a strong grasp of the existential threat posed by climate change.

But the heart attack is now a political problem — for him and the Democrats. It may not be possible for Bernie to continue pushing himself in the way he'd have to push himself to be nominated and to beat Donald Trump.

And beating Trump has become a national emergency. As recent weeks have shown, Trump is dangerously out of touch with reality, with no understanding of the constitutional separation of powers. Trump's behavior with regard to Ukraine (which is likely the tip of a proverbial iceberg) — and more blatantly, his invitation to China to interfere in America's election — makes it clear that he is willing to upend the democratic process itself, OUR democratic process, using his vast authority solely for his own, personal benefit.

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