The kickoff presidential debate Wednesday in Denver is shaping up as do-or-die time for Mitt Romney, with the pressure intensifying this week after a flurry of swing-state polls showed President Barack Obama opening up a sizable lead.

Republicans, fretting about dwindling days for Romney to turn around his campaign, fear that if their nominee doesn’t come away with a decisive first-debate victory, he’ll continue to spiral downward and lose his last, best shot for a comeback.

The fear among donors and strategists: a break-even or so-so performance would subject Romney to a self-reinforcing cycle of criticism and pessimism in his own party that will send other Republicans fleeing and make it difficult for Romney to project a closing argument against Obama over the drumbeat of why-are-you-losing questions