US President Donald Trump has privately acknowledged that Republicans could face a “worst-case” outcome in the midterm elections, despite occasionally expressing optimism that his party could outperform pre-election polls, a report says.

CNN carried the report on Tuesday, citing sources close to the president as voting is underway across the United States in elections that will determine whether Republicans retain control of both chambers of Congress or Democrats gain the power to obstruct Trump's legislative agenda during the final two years of his presidency.

Trump has made himself the center of the Republican campaign, holding rallies across several states and urging voters to support his party's candidates. However, his administration faces mounting concerns over the economy, the cost of living, and the political fallout from the war against Iran.

According to CNN's sources, Trump has privately conceded that Republicans could suffer a particularly damaging defeat, even as he has expressed hope that polling showing Democratic gains may be inaccurate.

Early exit polls released by the Associated Press identified the cost of living and government corruption as the two leading concerns among voters. Economic anxiety has been compounded by the war and Trump's tariff policies, while the administration has also faced criticism over its handling of inflation.

The election has also been accompanied by legal challenges involving the administration's efforts to address alleged “voter fraud.”

On Tuesday, a federal appeals court overturned an earlier order preventing administration officials from asking election workers to set aside ballots cast by people suspected of being “non-citizens.”

Voting machine problems and other disruptions were reported in several parts of the country, including in a closely watched New York congressional contest between Republican Representative Mike Lawler and Democratic challenger Cait Conley.

An unprecedented mobilization of election monitors and legal challenges has also raised concerns about potential disruptions and disputes over the results.

Republicans enter the elections with narrow majorities in both chambers. Democrats need a net gain of three seats to take control of the House of Representatives and four seats to secure a Senate majority, where Republicans currently hold a 53-47 advantage.

A Democratic takeover of the House would give the party control of key committees and greater authority to investigate the administration through hearings and subpoenas.

It would also increase Democratic influence over government spending, although Trump would retain his veto power.

If Democrats capture both chambers, Trump's legislative agenda could face considerably greater obstacles. Another impeachment effort could also emerge, although removing the president would require a two-thirds majority in the Senate.

Beyond congressional control, the results will also indicate whether Trump's gains among young, Black, and Latino voters in the 2024 presidential election have endured, as Democrats seek to rebuild support among these groups ahead of 2028.