The Republican presidential candidate, speaking to supporters in Ohio, made the claim after repeating his baseless assertion that his 2020 election defeat to Democratic President Joe Biden was the result of election fraud.
During an outdoor speech that was whipped by strong winds and punctuated by some profane language, Trump predicted that if he does not win the Nov 5 general election, American democracy will come to an end.
"If we don't win this election, I don't think you're going to have another election in this country," Trump said.
Trump, who is under criminal indictment in Georgia for trying to overturn the result of the 2020 election there, this week won enough delegates to mathematically clinch the Republican nomination.
A general election rematch with Biden is likely to be extremely close. A Reuters/Ipsos poll last week found the two candidates in a statistical tie with registered voters.
Trump opened his remarks in Dayton with a tribute to his supporters who are currently in jail for rioting at the US Capitol on Jan 6, 2021, as they sought to block certification of Biden's 2020 election win.
Trump saluted and called them "patriots" and "hostages".
In the middle of a section in his speech about placing tariffs on imported cars, and foreign competition for the US auto industry, Trump declared: "If I don't get elected, it's going to be a bloodbath for the whole country."
Asked what he meant, his campaign pointed to a post on the social media platform X by a New York Times journalist, which said Trump's "bloodbath" comment came amid a discussion about the US auto industry and the economy.
Asked for a response to Trump's "bloodbath" comment, Biden campaign spokesperson James Singer condemned Trump's "extremism", "his thirst for revenge", and his "threats of political violence".
Trump also appealed to Blacks and Hispanics, voters who will play a key role in deciding November's election.
Trump has been narrowing the gap with Biden in opinion polls with non-white voters, who formed a core part of Biden's winning coalition when he defeated Trump in 2020.
Trump cited a central campaign theme, that too many illegal immigrants have crossed the US-Mexico border since Biden took office, in his appeal to minority voters.
"No-one has been hurt by Joe Biden's migrant invasion more than our great African American and Hispanic communities," Trump said. He claimed without citing any evidence that illegal immigrants were taking their jobs.
