Democrats look set to extend their control of the US House of Representatives for two more years but with a potentially shrunken majority, as they lost at least six incumbents and failed to oust any Republicans in initial results.

By 3am EST (8am GMT), Democrats’ only gains were two North Carolina seats vacated by Republican incumbents after a court-ordered remapping made the districts more Democratic.

Though the Democrats seem likely to retain House control, the results are developing into a disappointment for the party, which had hoped to make modest gains of perhaps 15 seats.

After decades of trying, Republicans defeated 15-term representative Collin Peterson from a rural Minnesota district that backed US president Donald Trump in 2016 by 31 percentage points – Mr Trump’s biggest margin in any Democratic-held district.

Mr Peterson, who chairs the House Agriculture Committee, opposed Mr Trump’s impeachment and is one of the House’s most conservative Democrats. He was defeated by Republican Michelle Fischbach, the former lieutenant governor.

Freshmen Democrats Debbie Mucarsel-Powell and Donna Shalala lost, falling in adjacent South Florida districts in a state where Mr Trump seemed to consolidate his support among Cuban voters.

Also losing were Democratic freshmen Joe Cunningham of South Carolina, Xochitl Torres Small of New Mexico and Kendra Horn in Oklahoma, who had surprising victories in 2018 in districts Mr Trump carried decisively in 2016.

The fight for Ms Torres Small’s seat cost around 35 million dollars (£27 million), making it one of America’s most expensive races, according to the non-partisan Centre for Responsive Politics. She was defeated by Yvette Herrell, a former state legislator.

Democrats were also disappointed in the Senate, where they nursed fading hopes of winning the majority.

Before votes were counted, both parties’ operatives said the Republicans would be fortunate to limit Democratic gains to a modest single digits. Democrats control the House by 232-197, with five open seats and one independent. It takes 218 seats to control the chamber.

A smaller Democratic majority would make it tougher for House Speaker Nancy Pelosi to unite her legislators as a handful of progressive freshmen arrive for the new congress.

By retaining House control, Democrats would mark only the second time in a quarter century that they have led the chamber for two consecutive two-year congresses. The first period ran from 2007 through to 2010, when Ms Pelosi was serving her first four years in her post.

“Our purpose in this race was to win so that we could protect the Affordable Care Act and so that we could crush the virus,” Ms Pelosi told reporters, citing former president Barack Obama’s health care act.

She declared that Democrats had won the House majority, which seemed highly likely but had not been officially declared by The Associated Press.

Democrats’ hopes of protecting their majority and even expanding it were based on public anxiety over the pandemic, Mr Trump’s alienation of suburban voters and a vast fundraising edge. But those advantages did not carry them as far as they had hoped.

With party expectations for capturing the House all but non-existent entering US election day, Republicans were happy with the results.

“House Republicans have outperformed all expectations,” said Dan Conston, who heads the Congressional Leadership Fund, a committee aligned with House Republican leaders that provides millions to Republican candidates.

Democrats lost a series of what were viewed as coin-flip races, failing to defeat the incumbents in Cincinnati, rural Illinois, central Virginia and the suburbs of St Louis and two contests in Texas.

Some endangered Democrats like Texas’ Lizzie Fletcher and New Jersey’s Tom Malinowski and Andy Kim held on. But the party notched no initial victories in long-shot races that they had hoped would bolster their majority.

Republicans retained such districts in central North Carolina; Montana; Omaha, Nebraska; and around Little Rock, Arkansas.

As Wednesday morning progressed, other hotly fought races remained undecided in states including Georgia and Virginia.