Donald Trump delivered a campaign speech in Washington DC on Monday afternoon. (Reuters: Jonathan Ernst)

Sitting US presidents have historically faced a backlash at the midterm elections, with Donald Trump highlighting that trend as his party faces the possibility of losing control of Congress.

Mr Trump's approval ratings are particularly low right now.

Donald Trump has acknowledged his Republican Party is facing an uphill battle at the midterm elections this week, amid polling that suggests he could lose control of Congress.

In his final major campaign event before the elections, Mr Trump was quick to highlight the historical trend that the sitting president's party "doesn't win the midterms".

"But we gave this a very strong shot," he said during a speech in Washington DC on Monday afternoon, local time.

He later described the votes that would take place on Tuesday, local time, as "the most important midterm, I believe, in our lifetime".

"We have to keep our Congress strong and free," he said.

Analysts believe the GOP will be swamped in many House races, and while losing its Senate majority also remains a possibility, the contests in that chamber are considered more competitive.

Midterm elections are typically difficult for whichever party the president of the day represents.