Republican candidate Donald Trump was briefly rushed off the stage by Secret Service agents at a rally in Reno, Nevada, in a false alarm.
A man holding a sign saying Republicans Against Trump was tackled by security agents, after shouts that he had a gun.
Mr Trump returned to the stage at Saturday’s rally minutes later.
The Republican candidate says he is going to target states seen as Democratic strongholds ahead of Tuesday’s election.
Both candidates have been making late changes to their travel schedules as falling poll numbers for Mrs Clinton in some key Democratic-leaning states present what the Trump campaign sees as new opportunities.
However, a new NBC/Wall St Journal opinion poll on Sunday suggested a four-point lead for Mrs Clinton.
The latest Washington Post/ABC tracking poll puts her lead at five points.
Sunday’s campaign stops take Mrs Clinton to Ohio, Michigan, Pennsylvania and New Hampshire, while Mr Trump travels to Iowa, Minnesota, Michigan, Pennsylvania and Virginia.
‘There is no gun’
On Saturday evening, Mr Trump had stopped speaking at the Reno rally after seeing something in the auditorium.
He was grabbed by two agents, who rushed him off stage, while the protester was held down and searched.