If Republicans keep their majority, McCarthy could be the next speaker of the House.
Secondly, it could lead to a string of damaging congressional investigations being launched by House committees controlled by the Democrats, on everything from Mr Trump's tax returns to the business interests of his family. "You got to go out to vote".
Firstly, it would mean the party could block legislation proposed by the president.
For example, Ezra Klein, "the former wunderkind at the Washington Post, now a [t] Axios or somewhere, actually said - and I've never seen this".
A inquiry into the Russian Federation investigation, led by special counsel Robert Mueller, could be ordered by the House Judiciary Committee to determine if "impeachable" offences were committed by Trump, he said. "They think that they have been getting jobbed on elections left and right - and that if they lose this one, there are a bunch of them predicting total meltdowns", he said. "I think he's preying upon people's fears".
Control of the House of Representatives is expected to be determined by a few dozen districts, many of them in the nation's suburbs, and will offer clues to where Americans stand in 2018 on immigration, guns, healthcare and gender equality in the #MeToo era.
Nancy Pelosi, the Minority Leader of the United States House of Representatives, also agreed. They have come a long way in messaging.
Democrats need a net gain of 23 seats to take control of the House for the first time since the Tea Party wave of 2010 and the latest polls give them a good chance to do so. This will leave President Trump unable to pass key laws through the houses.
Current estimates suggest the Republicans have a 80.9 percent chance of keeping control and the Democrats have a 19.1 percent chance.
The president has vowed to continue pushing for significant funding for a border wall, which Republicans may feel more comfortable with backing if voters hand them power again.
With terms of six years, about a third of the Senate is up for election every two years. But they were just warmup acts for the main event, the blunt former presidential candidate Bernie Sanders, who while technically an independent is a champion of causes held dear by liberal progressive Democrats. But 23 is no sure thing: polls suggest their leads are narrow in numerous seats that could push them into the mid-20s or even the mid-30s.
"After 11 rallies in 8 states and weeks of campaigning for Republican candidates, the President will spend today making phone calls, monitoring Congressional, Senate and Gubernatorial races across the country and meeting with his political team for real-time updates", White House press secretary Sarah Huckabee Sanders said in a statement. "We should learn history to know that those things don't end well".
Both President Trump and his Attorney General Jeff Sessions warned of voter fraud and illegal voting in Tuesday's elections, even though such allegations in 2016 proved to be largely phony and aimed at glossing over the fact that he lost the popular vote by more than three million votes. We need to get better trade deals with our friends around the world. They can do whatever they want and I can do whatever I want'. Republicans hope he can help GOP Rep. Mia Love over the line in her toss-up race in the 4th District.
Trump, without control of Congress, could decide to triangulate.
"It could be bad for Republicans if he tries to do that", says Heye.
Executive Director for the Center for Responsive Politics Sheila Krumholz commented: "The significance of this election is clear".
What has President Trump being saying?
And on Monday in IN, he deployed three of his most prominent female supporters - press secretary Sarah Huckabee Sanders, adviser Kellyanne Conway and daughter Ivanka Trump - to help garner support among women, who are expected to turn out in droves on Tuesday.
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