Former US President Barack Obama has warned against rhetoric he said was designed to sow fear as he campaigned in support of Democratic candidates while President Donald Trump hammered a hardline anti-immigration message to energise Republicans.
Twitter has also said it deleted more than 10,000 automated accounts posting messages that discouraged people from voting in Tuesday’s elections and wrongly appeared to be from Democrats, after the party flagged the misleading tweets to the social media company.
The removals took place in late September and early October.
Mr Obama hit on a common theme of Democratic campaigns - defending the 2010 healthcare law that was his signature domestic achievement, while urging Americans not to embrace hostility and division in politics.
"We have seen repeated attempts to divide us with rhetoric designed to make us angry and make us fearful," Mr Obama said in Miami.
"But in four days, Florida, you can be a check on that kind of behavior."
Mr Obama was flanked by gubernatorial candidate Andrew Gillum, who faces former congressman and strong Trump backer Ron DeSantis, and Senator Bill Nelson, who is being challenged by the outgoing governor, Rick Scott.
Mr Trump's campaign stops were aimed at bolstering Republicans challenging incumbent Democratic senators in West Virginia and Indiana, states he won in the 2016 presidential election.
"This election will decide whether we build on the extraordinary prosperity that we've unleashed ... or whether we let the radical Democrats take a giant wrecking ball to America and to our future," Mr Trump said in West Virginia.
Opinion polls and non-partisan forecasters generally show Democrats as having strong chances of winning 23 additional seats and taking a majority in the House of Representatives, which they could use to launch investigations into Mr Trump's administration and block his legislative agenda.
Republicans are generally expected to retain control of the Senate, whose powers include confirming Mr Trump's nominations to lifetime seats on the Supreme Court.
Mr Obama's speech was repeatedly interrupted by hecklers, prompting him to quip, "Why is it that the folks who won the last election are so mad all the time?"
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Interest in the election has been unusually high in a year when Congress but not the White House is at stake, according to early voting tallies.
27 states plus the District of Columbia have recorded more early votes at this point in the campaign than they did in all of 2014, according to The Election Project at the University of Florida, which tracks turnout.
Texas had already recorded more votes than it did in all of 2014, including Election Day, the group said.
The final weeks of the campaign season have also seen a spate of violence including the shooting of 11 people at a Pennsylvania synagogue and more than a dozen package bombs sent to prominent critics of Mr Trump.
The FBI said yesterday it had recovered a suspicious package addressed to California billionaire Tom Steyer, a Democrat known for his ads calling for Mr Trump's impeachment.
