US President Donald Trump has warned Americans not to elect “jihadists” and “communists” in his final pitch before midterm elections on Tuesday (local time) as a new poll shows a blue wave sweeping through key battleground seats.

The latest New York Times and Siena College poll showed Democrats leading in seven crucial Senate races — Michigan, Kansas, Texas, Maine, Ohio, Alaska and Iowa.

In the battleground state of Michigan, high-profile Democrat Abdul El-Sayed, who has taken social media by storm, is leading opponent Mike Rogers by 11 percentage points (53 per cent to 42 per cent) — outside the poll margin of error.

The survey was done before the shock defection of Democratic Congresswoman Haley Stevens who announced she would back the Republican Rogers instead of party colleague El-Sayed.

Stevens, who lost the ‌Michigan Democrats’ Senate primary to El-Sayed in a bitterly contested race, turned up at a Detroit church with Rogers in what Democrats labelled a “betrayal”.

That same day, El-Sayed’s campaign announced it received $US 2.4million in donations, breaking its single-day fundraising record.

El-Sayed has come under repeated attack from Trump over his Muslim faith with comments such as: “I’m here to keep a jihadist Muslim Brotherhood member from becoming a United States senator.”

Trump on Sunday (local time) invoked the September 11, 2001, terrorist attacks, drawing a comparison between stopping El-Sayed from entering the Senate and the passengers who fought back against the hijackers aboard United Flight 93.

“Twenty-five years later, Michigan needs to stand up and fight, just like Todd did, to stop a jihadist from walking into the Capitol,” Trump said, referring to Todd Beamer, a Michigan native who died aboard the flight.

The son of an Egyptian immigrant and with a white Michigan stepmother, El-Sayed has become an online sensation for his bitey retorts to Republicans and his ability to cut through on major issues such as cost of living.

A former public health official, he has repeatedly said he is loyal to the US and disavowed the Muslim Brotherhood.

Stevens’ decision to endorse El-Sayed’s opponent surprised party leaders, with some members, such as representative Debbie Dingell, saying that it created a “distraction” for Democrats.

Stevens said in a video posted to social media: “I don’t belong in Abdul’s campaign.”

Trump on Tuesday morning (AEST) called the midterm elections the most important “in our lifetime” in his final pitch at the Lincoln Memorial Reflecting Pool in Washington DC.

He labelled the Democrats “dangerous” and warned that they would “blow-up” everything he had achieved.

Trump cautioned that sitting presidents usually struggle in the midterm elections as he said the United States has its most secure borders and largest income tax cuts in the country’s history.

“For some reason, the sitting president doesn’t win the midterms,” Trump said.

“But we gave this a very strong shot.”

Trump closed out the final weekend of a turbulent midterm election campaign with rallies in two states he had handily won in the past.

Trump was in Salina, Kansas, and Dubuque, Iowa, on Sunday.

Republicans in both states are fending off robust challenges from Democrats, threatening Republican majorities in the Senate while they’re already at risk in the House.

But in Iowa, Trump insisted Republicans were on the verge of sweeping victories on election day.

“We’re going to elect ‘America first’ Republicans up and down the line,” he said near the start of a speech that lasted two hours, long even for Trump who is known for his lengthy freewheeling rallies.

Later, he arrived tardy in Kansas, where Air Force One performed a theatrical flyover before landing for an outdoor rally at the airport.

Thirty-five Senate seats and all 435 House of Representatives seats are on the ballot, with first results starting to flow on Wednesday morning in Australia.

-with AAP/AP