He has also refused a second debate with Harris, after being soundly bested in the first.
But Harris, who turns 60 this weekend, hammered Trump over his health and resilience.
Dueling ralliesHe also claimed to be "killing" her in the polls and that she did not pass the bar exam.
But he was back on home turf Friday morning for a soft Fox News interview, before heading to Michigan for counterprogramming against Harris.
Both candidates are spending their final campaign days in pivotal battleground states where early voting is already underway.

'Unfit For World's Toughest Job': Harris Targets Trump After Report Of Exhaustion