Donald Trump suggested that if Hillary Clinton gets to pick US federal judges as president, there is nothing that can be done to protect the right to bear arms.
But then he added without elaboration that maybe supporters of the second amendment could figure out a way.
He said on Tuesday at a rally in North Carolina: "By the way if she gets to pick her judges, nothing you can do, folks. Although the second amendment people, maybe there is, I don't know."
It was not immediately clear what Mr Trump meant. His spokeswoman did not immediately reply to a request for a clarification of his remarks.
The Republican presidential nominee made the comment on Tuesday at a rally in Wilmington, North Carolina.
The second amendment provides a constitutional right to citizens to own guns.
During the event, he said falsely that Mrs Clinton "essentially wants to abolish the second amendment".
Mrs Clinton supports some new restrictions on gun ownership, but has not advocated overturning the amendment.
Mrs Clinton's campaign manager immediately denounced Mr Trump's remarks, saying the Republican nominee was trying to incite violence.
Robby Mook says: "This is simple - what Trump is saying is dangerous. A person seeking to be the president of the United States should not suggest violence in any way."
But Mr Trump's communications director Jason Miller said the celebrity businessman was referring to the "power of unification".
He said: "Second amendment people have amazing spirit and are tremendously unified, which gives them great political power. And this year, they will be voting in record numbers, and it won't be for Hillary Clinton, it will be for Donald Trump."