Democratic presidential hopeful Hillary Clinton launched an open appeal Wednesday to independents and Republicans repulsed by Donald Trump, after the party's nominee again sparked controversy with comments seen by some as a threat against her.

The latest Trump firestorm erupted when he suggested at a rally Tuesday in North Carolina that "Second Amendment people" -- those who support gun rights -- could take action to stop Clinton from appointing US Supreme Court justices as president.

After his comments were judged by many as courting violence, the Clinton team pounced by announcing a new "outreach to the growing number of Republicans and independents" who are prepared to vote for the former secretary of state on November 8.

The campaign unveiled a new website, togetherforamerica.com.

It lists dozens of Republicans and independents who back Clinton, including former director of national intelligence John Negroponte, former New York mayor Michael Bloomberg and Hewlett Packard Enterprise chief executive Meg Whitman.

"Americans are looking to the next president to help bring us together to tackle the big challenges facing the country, and Hillary Clinton's bipartisan support is the latest proof that she can work across the aisle to make us stronger together," campaign chairman John Podesta said in announcing the effort.

"Regardless of party, voters are increasingly concerned that Trump's tendency to bully, demean and degrade others sends the wrong message to our children."

Trump insisted that his "Second Amendment" comments referred to the power of gun rights supporters as a "political movement."

But lawmakers, former national security officials and other critics expressed concern that he had advocated violence, possibly in jest, against Clinton or her Supreme Court nominees.

"Hillary wants to essentially abolish the Second Amendment" of the US Constitution, Trump, 70, told a rally at the University of North Carolina.

"If she gets to pick her judges, nothing you can do, folks," Trump said.

"Although the Second Amendment people -- maybe there is, I don't know."

It was the latest in a long string of Trump missteps -- including his prolonged clash with the parents of a Muslim American soldier killed in action -- that have marred his campaign since he officially won the nomination last month, prompting several Republicans to reject his candidacy.

Former New York mayor and Trump backer Rudy Giuliani was forced into clean-up mode Wednesday, insisting the uproar was triggered by "the Clinton spin machine" and that Trump was indeed talking about the power of pro-gun voters to defeat her at the ballot box.

"What he intended was that they should vote against her," Giuliani told ABC.

The Secret Service said it was "aware of the comments" but did not say whether they merited an investigation, which some Democratic lawmakers have called for.

Trump has clearly roiled the party with his unorthodox campaign remarks, with Republicans frustrated at his apparent inability to stay on message even as he unveiled his revamped economic plan on Monday.

A Reuters/IPSOS poll released Wednesday found that 19 percent of Republican voters want the real estate tycoon to drop out of the race, while 70 percent think he should stay and 10 percent say they don't know.

The RealClearPolitics national poll average shows Clinton leading Trump by 48 percent to 40 percent.

Fifty prominent national security experts recently announced in an open letter that they would not vote for Trump, saying he "lacks the character, values and experience" to be president.

Six US senators including Susan Collins and a number of House Republicans have disowned him as well.

Dan Rather, the former CBS News anchor with half a century of political reporting experience, warned in a Facebook post that Trump's "Second Amendment" comments mark a "new low" in US politics, and that "history is watching."

"This cannot be treated as just another outrageous moment in the campaign," Rather said.

Meanwhile Clinton was enduring a fresh round of criticism over her emails from her time as secretary of state, which have been a thorn in her side throughout her campaign.

Conservative watchdog Judicial Watch released a batch of emails that raise questions about the State Department's relationship with the Clinton Foundation.

The Trump campaign seized on the latest emails to blast Clinton as "corrupt," with critics saying the messages showed the department and the foundation were engaged in improper preferential treatment