Republicans could be swamped by a “blue wave” in Congress, according to a clutch of polls which show double-digit leads for Democrats in November’s midterm elections.
Midwest voters are fuelling a growing gap between the two parties as support for Donald Trump wanes in key states such as Michigan, Wisconsin and Minnesota, one pollster said.
“Every way we are looking at the data, the same general pattern is emerging,” said Lee Miringoff, director of the Marist Institute for Public Opinion, whose latest survey showed a 12 percentage point lead for the Democrats.
“The Midwest is an area that is getting restless about what they hoped was going to occur and what they feel is not occurring,” he added.
A separate poll published on Wednesday by Quinnipiac University showed a 14-point advantage for the Democrats, while a Politico and Morning Consult survey put the party 10 points ahead.
All three polls asked voters whether they preferred the Democrat or Republican in their district, rather than about specific candidates.
Democrats need to gain 23 seats in the 6 November elections to seize control of the House of Representatives and the power to thwart President Trump’s agenda.
Historically the sitting president's party tends to lose seats in congressional midterm elections and some analysts believe Mr Trump's low national approval rating will impact upon Republican candidates.
“Republicans have not only been fairly silent in opposition to the president, but they’ve been driving very hard in the Senate when it comes to his Supreme Court nominee,” Mr Miringoff told NPR, which commissioned Marist’s research. “In terms of brand, they look totally in lockstep with the president – and that has become extremely clear to voters.”
Polls in July suggested only a third of voters in Michigan, Wisconsin and Minnesota thought Mr Trump deserved a second term as president.
Mr Trump’s waning support in the Midwest may be linked to the trade wars he has waged with other nations. The region’s farmers and car manufacturers have been hurt by tariffs imposed on exports in retaliation for the president ramping up import duties.
Half of US voters surveyed by NPR/Marist said they were more likely to vote for the Democrat in their congressional district, compared to 38 per cent who opted for the Republican.
The Politico and Morning Consult poll found 45 per cent preferred their Democrat candidate, compared to 35 per cent Republican.
The split in Quinnipiac University’s survey was 52 per cent to 38 per cent.
“By a 14-point margin, Americans would rather vote for the Democratic candidate in their local race for the US House of Representatives. Could the ‘blue wave’ become a tsunami?” said Tim Malloy, assistant director of the Quinnipiac University research. ”There are a lot of factors, and eight weeks of campaigning, that make up the answer to that question.”
The Quinnipiac poll found 72 per cent of voters disapproved of the job US Congress was doing, and 58 per cent felt the house should be more of a check on Mr Trump.
"Whoever wins, they're going into a Congress with an abysmal approval rating," said Mr Malloy.
Census Bureau data published on Thursday contained one sign of hope for Mr Trump, with incomes posting strong growth last year in more than a dozen US congressional districts where Republicans face stiff challenges in the midterms.
The bureau's annual American Community Survey showed that median incomes grew 6 per cent or more in 14 battleground districts, more than a percentage point higher than nationwide gains.
All 14 districts are held by Republican candidates, who have made the strengthening US economy a dominant theme of their campaigns.
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