To be great, politicians – like athletes, performers and mythic heroes – must rise to moments of great challenge. Hillary Clinton’s moment comes in Monday’s debate.

The merciless beast Momentum has turned against her. It was with her for several weeks after the conventions. Then the media and the commentariat grew tired of talking about how truly awful Donald Trump is and would be as President. They turned their fire to Hillary:

She didn’t tell us she had pneumonia! Calling Trump voters “deplorables” was a gaffe! She can’t put the email scandal behind her! People don’t like her, her voice, her hair, her clothes! She doesn’t excite minorities and millennials the way Obama did!

Monday night, head to head with Trump, Clinton can turn it all around. For all the criticisms of her political skills, this is an arena where she has excelled.

In unscripted – and combative – settings, her warmth and her toughness both come through. Like when she faced down Republicans on the Benghazi committee.

Her knowledge, temperament and judgment – shaped by decades of policy and government work – come through.

Most of all, the X-ray of TV will let us see through two possible Presidents.

And one of them is Donald Trump.