Trump announced the "general news conference" in a one-sentence post on his Truth Social platform after Harris and new running mate Tim Walz have drawn large, jubilant crowds for her freshly energized Democratic bid to beat Trump in November.
Since President Joe Biden dropped out of the race last month, Harris has turned the race for the White House upside down, raking in donations and erasing Trump's lead in the polls.
Trump is described in U.S. media reports as angry at how his campaign is now performing against Harris and how it dominates news coverage.
He is also reportedly unhappy with his young Republican running mate J.D. Vance, who has been described as a lackluster public speaker and making a poor impression with voters.