Republicans and Democrats were making frenzied, final pushes Sunday to motivate their voters ahead of midterm elections seen as a referendum on President Donald Trump's divisive first two years in office.
With political passions at a rare peak, early voting in some states already running far ahead of normal levels.
He appeared on "Fox News Sunday". And with Democrats favoured to retake the House of Representatives, Republican National Committee chair Ronna McDaniel concurred that: "It's going to depend on voter turnout on Election Day."
But in the first mid-term under Trump -- an utterly unconventional president -- there are many unknowns, above all the bottom-line impact of a president who has driven both supporters and foes to a rare fever pitch of emotion.
The party of a first-term president tends to lose congressional seats in his first midterm. But a healthy economy tends to favour the incumbent -- and the US economy has been growing with rare vigor.
A new Washington Post-ABC News poll on Sunday suggested that while Democrats retain an edge in their battle for the House, Republicans could profit from increasingly positive assessments of the economy and by Trump's harsh focus on border security.
It found registered voters preferred Democratic candidates for the House over Republicans by 50 percent to 43 percent; but that was down from a 14-point advantage in August.
Another wild card: The campaign's closing days come just a week after a gunman, who allegedly hated immigrants and Jews, killed 11 people at a Pittsburgh synagogue, and after a fanatical Trump supporter was arrested in Florida on charges of mailing pipe bombs to prominent Trump opponents, including Obama.
The president's critics say the highly charged atmosphere he has helped create made the two attackers feel comfortable to carry out their crimes. Republicans, trying to move past that, have been enthusiastically pressing the economic argument.
American voters have watched the economy grow for two years under Trump, McDaniel said on ABC. "They're making more money. More jobs are coming back. That's a great closing argument."
But the president -- to the unease of some in the party -- has instead used his nearly nonstop schedule of campaign rallies to keep the spotlight on what he calls the security threat from migrants seeking to enter the US through Mexico.
Democrats meantime insist that only they will protect the healthcare gains made under President Barack Obama, that Trump has employed inhumane measures to keep migrants out, and that the divisiveness he has fostered must end.
"The Republican effort to take away important healthcare protections is one that Senate Republican candidates have been running away from," Van Hollen, who heads the Democratic Senatorial Campaign Committee, said on ABC.
But he was cautious about prospects for his chamber on Tuesday, saying, "Senate Democrats really face the toughest political map in 60 years.