The comments marked the starkest indication that Trump has grown less optimistic about the GOP's chances of retaining control of the House, where Republicans face greater headwinds than in the Senate.
Democrats are drawing strength from women and college-educated voters in general, who swung decidedly against Trump since his election.
Democrats face a far more hard challenge in the Senate, where they are nearly exclusively on defense in rural states where Trump remains popular.
President Donald Trump speaks during a rally at Southern Illinois Airport in Murphysboro, Ill., Oct. 27, 2018.
"Democrats want to invite caravan after caravan of illegal aliens to pour into our country".
The US president has framed migrant caravans approaching through Central America as an existential crisis for country, calling it an "invasion" and dispatching more than 5,000 soldiers to the border. "And they want to erase America's borders", Trump told a raucous rally in Chattanooga, Tennessee late Sunday. "I'm here to say that hatred is not going to win".
Meanwhile his staff has begun preparations to deal with a flood of subpoenas that could arrive next year from Democrat-controlled committees and the White House counsel's office has been trying to attract seasoned lawyers to field oversight inquiries. A CNN poll gave Democrats the largest margin, a 13-point advantage; an NBC/Wall Street Journal poll had the Democratic lead at 7 points.
"The vast majority of women voters are angry, frustrated and they are really done with seeing where the Republican Party is taking them, particularly as it related to heath care and civility", said Stephanie Schriock, who leads EMILY's List, a group that help elect Democratic women. But I always voted, and you should too. When you participate in the political process, you can be a check on bad behavior.
"You're going out there, you're going to make sure that people vote to start making things better", Obama said.
The roadmap for this year's strategy was drawn last year by Virginia Democratic gubernatorial candidate Ralph Northam, who handily defeated Republican Ed Gillespie by emphasizing economic issues while Gillespie stoked fear among voters over immigration and crime - much like Trump at his late-stage campaign events.
Asked about the ad on Monday, Mr Trump told a journalist: "A lot of things are offensive".
Parag Thatte, equities strategist at Deutsche Bank in NY says: "Our trading desk thinks betting on volatility reducing after the election would be a good trade right now". Another compared Donald Trump with Russian President Vladimir Putin.
All politics may be local, but this year President Trump is nationalizing them - and key close races across the nation tomorrow will serve as harbingers of the national political climate. "I think there will be no difference here".
There are very obvious downsides to Republicans' losing the House for Trump.
FILE - People stand cast their ballots ahead of the November 6 election at Jim Miller Park, in Marietta, Ga., Oct. 27, 2018. At the same time, he has sought to distance himself from any potential blame if Republicans lose control of the House.
So you think President Trump is exceptionally unpopular?
But a House loss will prompt GOP hand-wringing about the divides in the party and the struggles for moderate Republicans to run in the Trump, as well as raise questions about whether the Democratic gains point to a path for presidential hopefuls in 2020.
What's clear is that there is more voter enthusiasm than usual among both Democrats and Republicans.
"Under the expectation that Republican voters typically are more likely to turn out, can Democrats energize people who identify with the Democratic Party to turn out and vote for their candidates?"
A Democratic House victory would also serve as a warning to Republican officeholders about their policies, their devotion to the president, and the brand of campaigning they have chosen this time.
"The House has been a rubber stamp for the Trump agenda". "Anything that gets done will have to be a bipartisan basis".
In the final stretch, Trump has ramped up his hard-line rhetoric on immigration and cultural issues, including warnings about a caravan of migrants headed to the border with Mexico and "liberal" mobs, and touted a growing USA economy that he said would be threatened by Democrats.