The president was responding to chants of "Fire Fauci" at a Florida rally.
President Donald Trump and former Vice President Joe Biden are racing toward Election Day with Biden in Pennsylvania and Trump Michigan, Iowa, North Carolina, Georgia and Florida on Sunday.
Vice President Mike Pence is in North Carolina and Sen. Kamala Harris, D-Calif., is in Georgia and North Carolina.
In the season's final ABC News/Washington Post polls, the pandemic versus the economy defines the presidential contest in two key battlegrounds, with Florida holding firm to its toss-up status while Biden leads slightly in Pennsylvania.
There's little change in either state. In Florida, Donald Trump has 50% support among likely voters to Biden's 48%; it was 51%-47% in an ABC/Post poll Sept. 20. Trump won the state by 112,911 votes out of more than 9.4 million cast in 2016.
In Pennsylvania, the race stands at 51%-44%, Biden-Trump, a 7-point advantage for the Democrat; that compares with a 9-point margin late last month. Here, Trump's 2016 win was even narrower: 44,292 votes out of nearly 6.2 million cast.
Additional non-scalable temporary fencing is expected to be erected around the White House perimeter in advance of Election Day, a federal law enforcement source confirms to ABC News.
The fencing is expected to go up beginning Monday.
Additional fencing has already been put up around Lafayette Square, just north of the White House.
-ABC News' Jack Date
The FBI, in a statement Sunday, confirmed it is investigating an incident on Friday where a campaign bus carrying Biden supporters was surrounded by Trump supporters in their vehicles while the bus was driving on a Texas highway.
"FBI San Antonio is aware of the incident and investigating," the FBI field office in San Antonio said. "No further information is available at this time."
President Trump responded to the announcement in a tweet Sunday night, saying, "In my opinion, these patriots did nothing wrong," and suggesting that the Bureau should instead be investigating left-leaning agitators.
Earlier Trump on Saturday approvingly tweeted out video of the Friday incident, saying, 'I LOVE TEXAS!" He separately claimed, falsely, at a later campaign rally that his supporters were merely "protecting" the bus.
Social media posts from those purporting to be a part of the so-called "Trump Train" group involved in the incident, however, show them clearly celebrating the effort as a confrontation with their political opponents.
The incident occurred Friday in Hays County when the bus, which was not carrying Biden or Harris, was traveling on I-35 between San Antonio and Austin.
According to the Texas Tribune, the actions led the Texas Democratic Party to cancel three campaign events they had scheduled in the state. Among those on the bus, according to the Tribune, was former state senator Wendy Davis, Rep. Lloyd Doggett and Travis County Democratic Party Chair Katie Naranjo.
-ABC News' Alexander Mallin
President Donald Trump is denying a report that he plans to declare victory Tuesday before all results are in, calling the report "false."
However he continued to press to have all of the ballots counted on Tuesday night, claiming, without evdence, that ballots counted after the polls close would be more open to fraud.
"As soon as that election's over, we're going in with our lawyers," Trump said.
Vice President Joe Biden was asked by reporters earlier about the possibility that Trump would declare victory on Nov. 3, even before all of the votes were reported by state election officials.
"My response is the president's not gonna steal this election," the Democratic nominee said.
Election results are not certified until all of the ballots, including absentee ballots, are counted, even if a candidate declares victory.
Biden also denounced the group of Trump supporters in Texas who appeared to aggressively tail and harass a Biden campaign bus on Friday. The FBI is investigating the incident, which was praised by the president and his allies.
"We've never had anything like this. At least, we've never had a president who thinks it's a good thing," Biden said. "Folks, this is not who we are. We are so much better than this."
-ABC News' John Verhovek and Elizabeth Thomas
Official election results likely won't be known until highly-contested states have counted all of their mail-in ballots, yet President Trump continued to press for the final results to be known on Election Day.
During a rally in Dubuque, Iowa, this afternoon, Trump insisted that a winner of the presidential election should be known on the evening Nov. 3, falsely saying "that's the way it's been."
Trump's own 2016 election victory was called around 2:30 a.m. the morning after Election Day.
Deadlines for receiving mail-in ballots also extend past Nov. 3 in several states.
-ABC News' Terrance Smith and Justin Gomez
