A poll of 1,000 voters run by NBC News and the Wall Street Journal shows Democrats still leading the race in the House of Representatives by seven percentage points, with voting preferences at 50 percent against Republicans, at 43 percent.
However, this result shows a curb in the support for the centre-left wing party since last month, when it could boast a nine-percentage-point lead.
This change was explained by analysts as a rising interest in the midterm election from Mr Trump’s base – white and older men coming mainly from rural areas.
The US president, they explained, successfully grabbed their attention through rallies around the country and promises to slash immigration.
Republican pollster Bill McInturff, who conducted the NBC/WSJ survey with his Democratic counterpart Peter Hart, said: “There has been some method to his madness. The base is coming home.
“Republicans have clearly made progress.”
The reignited interest in this round of election of Mr Trump’s voters means bad news to the Democrats, who need a two-seat gain to regain the majority in the House.
The party also has to avoid defeats in states with large rural areas, such as North Dakota and Indiana, where Mr Trump’s base is growing louder.
The telephone poll was run between November 1 and 3, just days after Washington unveiled the first section of the wall at the southern border between Mexico and the US.
And earlier this month, the Pentagon announced “more than 7,000” troops were being sent to the border to face the migrant caravan marching across Central America towards the US.
The migrant caravan started forming on October 12 in Honduras, where a group of 160 people set off on a long journey to the United States.
The caravan has since gathered thousands of people, including women and children, who prefer marching in group to be safer.
Despite the difficulties of determining how big the group is, the United Nations said that more than 7,000 people had joined the caravan since October 22.
Since its constitution, Mr Trump has attacked the people part of the migrant caravan, telling them to “turnaround”.
He wrote on Twitter: “To those in the Caravan, turnaround, we are not letting people into the United States illegally.
“Go back to your Country and if you want, apply for citizenship like millions of others are doing!”
He also claimed, without evidence, that among the migrants “invading” the US there are gang members and “bad people”.
He wrote: “Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border.
“Please go back, you will not be admitted into the United States unless you go through the legal process.
“This is an invasion of our Country and our Military is waiting for you!”
435 seats are up for grab in the House, while only 35 US Senators will be elected on November 6.
A victory of the Democrats in the Senate is deemed highly unlikely, with only a 15 percent chance of winning, according to polling site FiveThirtyEight.