Here's how Gardner can still win-
The only way Gardner can win is to condemn Trump, switch to independent, and apologize for the last six years when he was a Cocaine Mitch stooge.
Not even that. Republicans would abandon him in this scenario. Even if he played some sort of Never Trumper or basically be Mitt Romney over past few years, he would either have been primaried with the God Emperor's blessing (most likely) or Republicans/Trump voters just wouldn't vote for him in November. The few independents or Democrats he would get in return wouldn't make up the loss, let alone putting him over the finishline to defeat Hick (or any credible challenger).