Former U.S. President Donald Trump proposed three September debates against Vice President Kamala Harris on Thursday as he sought to wrest back some of the attention lavished on his rival since her blockbuster entry into the presidential election.

Harris has ignited the Democratic ticket in the last 18 days, pulling in record fundraising and obliterating the Republican ex-president's polling lead to open up a much broader path to victory than her party would have dared to hope for just a month ago.

The country's first female, Black and South Asian vice president heads into the Democratic National Convention in Chicago later this month on the back of a series of packed rallies that have won plaudits for a positive message that has reenergized the base.