Hillary Clinton has warned that Donald Trump's comments about supporters of the US Constitution's Second Amendment - which guarantees the right to bear arms - are just another example of how his words could have "tremendous consequences".
Democratic candidate Mrs Clinton said her Republican rival's remarks were a "casual inciting of violence" that show he lacks the temperament to be the American commander-in-chief.
She then noted her growing list of Republican supporters, saying they were backing her "not as Republicans, but as Americans".
Speaking to supporters in Des Moines, she said: "We may not agree on everything, but this is not a normal election.
"I will work hard for the next three months to earn the support of anyone willing to put our country first."
On Tuesday, Mr Trump falsely said that Mrs Clinton wanted to revoke the right to gun ownership.
He then said that there was nothing people could do to stop Mrs Clinton from stacking the Supreme Court with anti-gun justices, before stating vaguely that "although the Second Amendment people, maybe there is - I don't know. But I'll tell you what: that will be a horrible day".
Democrats quickly jumped on the comments as further evidence that Mr Trump is undisciplined and unprepared for the presidency, while Mr Trump insisted he was never advocating violence against Clinton.
As he struggled to turn the page on a difficult period in his campaign, Mrs Clinton's campaign continued a push to win over Republicans and independents, launching a group called "Together for America".
The group aims to use a wave of nearly 50 recent endorsements by high-profile Republicans and independents to convince voters to cross party lines.
The campaign released new endorsements from several retired Republican officials, including former commerce secretary Carlos Gutierrez, former housing and urban development secretary Carla Hills, former Maryland Congresswoman Connie Morella, former Connecticut congressman Chris Shays and former director of national intelligence John Negroponte.
Mrs Clinton will continue her appeals to Republicans and independents on Thursday with an economic speech in Detroit.
In Iowa, she stressed her commitment to small businesses and young entrepreneurs with a visit to local T-shirt store, Raygun.
The Iowa trip marked Mrs Clinton's first visit to the battleground state since her narrow win over Bernie Sanders in the lead-off caucuses.
She has had a troubled relationship with the state since losing here to then-senator Barack Obama in the 2008 caucuses.
Donald Trump has also focused heavily on Iowa, making several trips in recent weeks. Iowa has six electoral votes, with 270 needed to win the presidency.