Trump's remarks also prompted a rebuke from some fellow Republicans, particularly those looking to steer the party in a different direction in a post-Trump era.
Early voting — whether in-person or by mail-in or absentee ballot — has swelled during the COVID-19 pandemic as voters have sought the safety and convenience it offers.
Trump told Fox News Channel this weekend it's too early to make such an ironclad guarantee and scoffed at polls showing him lagging behind Democrat Joe Biden.