US voters will elect all 435 seats of the House of Representatives and just 35 of the 100 seats in the Senate.
Democrats would need a net gain of 24 seats in the House and two in the Senate to take majorities away from Mr Trump’s fellow Republicans.
Over the last 50 years, the Democrats have only scored a net gain of that size twice, once in 1974 and in 2006.
In 2006, the Democrats pulled in 31 seats in the midterm elections and regained control of the House during President George W Bush’s second term.
If they won the House and Senate it would put them in a position to oppose the president’s legislative agenda.
Opinion polls and political forecasters generally show Democrats having a strong chance of winning a House majority, with Republicans expected to keep control of the Senate.
According to a YouGov polls released at the Hoover Institution, a conservative think tank in California, the Democrats lead the Republicans nationwide by 54 percent to 46 percent.
This is enough to take 225 seats and claim a narrow majority in the House.
The Republicans hold a narrow 51-49 majority in the Senate and 10 incumbent Democrats are defending states that Donald Trump won in 2016.
Doug Rivers, chief scientist at YouGov global polling, said: “The chances of the Democrats winning all of those seem to me pretty slim.
“You need a wave where all the toss-ups essentially go one direction and then Democrats need to pick up two more seats to get a majority.
“There’s a rather good opportunity in Tennessee, Nevada and Arizona and then the long shot, which would be catastrophe for the Republicans, would be Texas.
“I don’t think the math adds up for a change. That would be more shocking than Trump winning the 2016 election.”
What will Democrats win in Senate and House mean for Trump?
The Democrats would have to take control of both chambers of Congress – the Senate and the lower House of Representatives – to take control of the legislative agency and block Trump’s ability to implement his programmes.
If the Democrats do take a majority, Mr Trump may struggle to push through any major legislative victories in the last two years of his first term.
For bills to be passed, they require a majority of votes in the House and if the Democrats gain a majority, they could potentially prevent bills supported by Mr Trump from going forward.
There is also a danger the president could face impeachment proceedings if Democrats take a majority in Congress.
However impeachment requires a two-thirds majority in the Senate, so would require Republican votes even if the Democrats won every available seat in November.
Many incumbent Republican House members have chosen not to stand and contest their seats in November.
Historically, American voters have tended to leave incumbents in place so the news 39 Republicans are not running for re-election could pave the way for Democrat candidates to be voted in.
Some of these seats are in key swing states such as Florida and Pennsylvania.