Kamala Harris's election campaign says it has raised $US200 million ($A305 million) and signed up 170,000 new volunteers in the week since she became the Democratic Party's presidential candidate, as Republicans continued to hammer Harris over her work as vice president.
President Joe Biden ended his reelection bid on Sunday last week and endorsed Harris for the November 5 vote against Republican former President Donald Trump.
"In the week since we got started, @KamalaHarris has raised $US200 million ($A305 million) dollars. 66 per cent of that is from new donors. We've signed up 170,000 new volunteers," Harris' deputy campaign manager, Rob Flaherty, posted on X.
Polls over the past week, including one by Reuters/Ipsos, show Harris and Trump essentially tied, setting the stage for a close-fought campaign over the 100 days left until the election.
Trump's campaign said in early July that it raised $US331 million ($A505 million) in the second quarter, topping the $US264 million ($A403 million) that Biden's campaign and its Democratic allies raised in the same period.
Trump's campaign had $US284.9 million ($A434.5 million) in cash on hand at the end of June while the Democratic campaign had $US240 million ($A366 million) in cash on hand at the time.
Harris has secured support from a majority of delegates to the Democratic National Convention, likely ensuring she will become the party's nominee for president next month.
"So our vice president is the presumptive nominee. We will have the official vote on August 1," Democratic National Committee Chair Jaime Harrison told MSNBC on Sunday.
Biden withdrew from the race amid questions about his age and health following a faltering debate performance against Trump in late June. Biden pledged to remain in office as president until his term ends on January 20, 2025.
Harris' takeover has re-energised a campaign that had faltered badly amid Democrats' doubts about Biden's chances of defeating Trump or his ability to continue to govern had he won.
Polls showed that Trump had built a lead over Biden, including in battleground states, after Biden's disastrous debate performance, but Harris's entry to the race has changed the dynamic.
A New York Times/Siena College national poll published Thursday found Harris has narrowed what had been a sizeable Trump lead while Trump had a two percentage point lead over her in a Wall Street Journal poll published on Friday. A Reuters/Ipsos poll published on July 23 showed a two point lead for Harris.
Republican attacks on Harris, the first woman and first black and South Asian person to serve as US vice president, have intensified in the days since she became the Democrats' likely presidential nominee.
Florida Governor Ron DeSantis, who vied unsuccessfully for the Republican nomination before endorsing Trump, told Fox News that Harris was "incredibly vapid" and predicted Democrats would issue "a blizzard of lies" to distance Harris from the Biden administration's policies on immigration and other issues.
"They have to whitewash Harris's background to be able to make her palpable to the American people," he said.
Some Trump allies, including some members of the "Black Americans for Trump" coalition, warn that disparaging Harris could hurt the former president in his outreach to black voters, a crucial demographic in the November 5 presidential election.
Harris's campaign had no immediate response to the DeSantis comments.
Mitch Landrieu, a campaign co-chair, told MSNBC that Harris "had one of the best weeks that we've seen in politics in the last 50 years".
"This is going to be a very close race," he said.
Trump's fundraising surged when he was convicted in late May on felony charges related to a hush-money payment to a porn star ahead of the 2016 election. An assassination attempt against him this month was also expected to spur campaign contributions.
