Harris has taken almost no questions from reporters since entering the race for the White House on July 21, and Trump is seeking to turn her lack of media exposure into an election issue as she surges ahead in polling and draws blockbuster crowds.
The Republican ex-president announced a "General News Conference" at his estate in Florida, after attacking Harris for not sitting down for an interview since she replaced President Joe Biden at the top of the Democratic ticket.
"Kamala refuses to do interviews because her team realizes she is unable to answer questions, much like Biden was not able to answer questions," Trump posted on his Truth Social Network.
"He is just plain 'shot,' and she is just plain 'Incompetent.'"
Trump -- who has held no public events this week -- also complained about media reporting on Harris's crowd sizes and accused Harris baselessly of paying for supporters to show up.
He teased an announcement about a presidential debate, saying: "I will expose Kamala during the Debate the same way I exposed Crooked Joe, Hillary, and everyone else during Debates. Only I think Kamala will be easier."
Trump backed out of an ABC News presidential debate scheduled for September 10 after Harris became his opponent.
In recent weeks, Harris has spoken off the record and answered just one question during an official appearance with Biden, while Trump appears regularly on friendly mainstream news shows and social media channels.
He made a contentious appearance at the National Association of Black Journalists (NABJ) convention last week, but didn't engage with the toughest questions, instead attacking his interviewers.
Harris has ignited her campaign in the last 18 days, pulling in record fundraising and eliminating the poll lead that Trump built up against Biden with her simple message: "We're not going back."
Her campaign reported raising $81 million in her first 24 hours in the race, and $36 million in the 24 hours after her announcement of her running mate, Minnesota Governor Tim Walz, on Tuesday.
Three months out from election day, she and Walz are barnstorming the battleground states, appearing Thursday in Detroit, Michigan before heading to the racially diverse "Sun Belt" states of Arizona and Nevada for rallies on Friday and Saturday.
The Harris campaign has launched a media blitz targeting Latino voters with an ad spotlighting Harris's personal story.
"As the daughter of an immigrant mother, like our community, Vice President Harris knows the power of determination," campaign spokesman Kevin Munoz said.
Sabato's Crystal Ball, a leading election forecaster, shifted its ratings in favor of Democrats on Wednesday, moving Minnesota and New Hampshire from "leans Democratic" to "likely Democratic" and Georgia from "leans Republican" to "toss-up."
Meanwhile Marquette University Law School released a nationwide survey showing that, among likely voters, Harris now leads Trump by six points -- 53 percent to 47 percent.
Trump and Vance have struggled to come up with effective attack lines to define Harris or Walz, although they have seized on the progressive records of both and have targeted supposed questions over Walz's military record.
Trump -- confronted on Vance's poor polling -- has pointed out that vice-presidential candidates rarely affect elections.
But Democrats have raved about the "joy" Walz has brought to an already exuberant campaign.
"Campaigns are all like roller coasters. You're either holding on for dear life or having the time of your life," Democratic strategist Caitlin Legacki posted on X. "Right now, we are having a blast."