Republican presidential candidate Donald Trump's campaign is launching a $10 million advertising campaign in six key states this week, hoping to counter growing voter interest and donations in Democratic rival Kamala Harris.

It's Trump's biggest ad buy since January, when he battled Republican rivals for the party's nomination. Trump's campaign did not respond to requests for comment, but the blitz comes as Harris' candidacy has changed the race.

Since President Joe Biden dropped out last week and endorsed Harris, she has quickly gained support from within the Democratic Party and major donors. She has also re-energized groups like young voters that Biden struggled to win over.

After months of criticism of Biden's fitness for office, Trump's campaign had to come up with a new message to use against the younger and more dynamic Harris, 59, who is less than 100 days away from the Nov. 5 election.