Candidates Barnstorm Battleground States on Final Friday of 2016 Presidential Race

— -- With a mere four days until Election Day, the presidential candidates visited three separate battleground states as they looked to shore up their base and reach out to any remaining undecided voters.

The latest ABC News-Washington Post tracking poll shows a tight race between Republican nominee Donald Trump and Democratic nominee Hillary Clinton. The poll finds a 47-44 percent race between Clinton and Trump in a four-day average among likely voters.

On Friday, Trump campaigned in New Hampshire, Ohio and Pennsylvania. Clinton, meanwhile, held events in Pennsylvania, Ohio and Michigan, a traditionally blue state that the Trump campaign hopes to turn red this year. Clinton's visits to Michigan and Pennsylvania are a sign the Democrat is looking to protect her firewall of states she hopes will help put her over the 270 electoral vote threshold to win on Tuesday.

Speaking in Atkinson, New Hampshire, Trump waxed nostalgic about his win in February’s primary there, “You know this is where it all began New Hampshire. ...This was our first victory and I never forgot that.”

But Trump didn’t miss an opportunity to lash out at his opponent, even raising the specter of former President Bill Clinton’s impeachment while attacking Hillary Clinton’s email controversy.

“If she were to win, it would create an unprecedented constitutional crisis. What a mess,” Trump said. “We went through it with him with the impeachment and the lies. Aren't we tired of this stuff?”

Hillary Clinton held her first campaign event of the day at Heinz Field, the home of the Pittsburgh Steelers, urging the crowd, “If you know anybody here in Pittsburgh or in western Pennsylvania who’s thinking about voting for Trump, please stage an intervention before it’s too late."

Their running mates also had busy days: Both GOP vice-presidential hopeful Mike Pence and Democratic running mate Tim Kaine spent time in Florida today. Pence also visited North Carolina and Michigan.

ABC News rates New Hampshire and Pennsylvania as leaning Democratic and Ohio as leaning Republican. Tossup races include Arizona, Florida, North Carolina and Maine’s 2nd congressional district.

More than 34 million Americans have already cast their ballots, according to data from The Associated Press. Republicans appear to be making up ground in some key swing states, including Arizona, Colorado and Nevada, bouncing back to 2012 early voting levels after a slow start in some states, and surpassing past early voting levels in others.

There has also been some improvement over 2012 for the GOP in North Carolina and Florida, and positive signs continue for the GOP in Ohio and Iowa. Even so, Clinton's campaign appears to maintain a grip so far on key states to win the 270 electoral votes that would put her in the White House.

ABC News' Gary Langer, Gregory Holyk, Chad Kiewiet De Jonge and Sofi Sinozich contributed reporting.