Voters in the United States headed to the polls on Tuesday in crucial mid-term elections that will determine if President Donald Trump’s Republican Party is able to retain control of the House of Representatives and the Senate, The New York Times reported. Elections to 36 state gubernatorial posts and state legislatures are also being held. Polling will close at 4.30 am on Wednesday (Indian time) in the eastern states and at 11.30 am in the westernmost parts of Alaska.

In Congress, Americans will elect all 435 members of the House of Representatives and 35 of the 100 Senate seats. Democrats need to pick up 23 seats to win control of the House but are at a disadvantage in the Senate, where a number of incumbents are defending their seats in states where Trump won the presidential polls.

Both Trump and Attorney General Jeff Sessions on Monday warned about the threat of voter fraud, echoing the president’s claim that massive voter fraud had marred his 2016 election. Trump had formed a commission to study the matter after he took office. But states refused to turn over voter data and it was disbanded soon after.

“Law enforcement has been strongly notified to watch closely for any illegal voting which may take place in Tuesday’s election (or early voting),” the US president tweeted on Monday. “Anyone caught will be subject to the maximum criminal penalties allowed by law. Thank you!”

In a statement, Sessions talked about the Justice Department’s plans to monitor ballot access and said “fraud in the voting process will not be tolerated”.

Voting rights advocates told The Washington Post that these remarks were attempts to intimidate voters ahead of the elections. Republicans, they alleged, curtail voting access with rules that disproportionately affect voters of colour, who tend to vote for Democrats.

“I find this kind of conduct incredibly anti-patriotic,” said Kristen Clarke of a voting rights group called Lawyers’ Committee for Civil Rights Under Law. “At a time when we need our White House and Justice Department speaking out against the relentless campaign of voter suppression in this election cycle, it defies reason.”

Hillary Clinton, the Democratic presidential candidate in 2016, said it was time for Americans to say “enough” after two years of watching the Trump administration “attack and undermine our democratic institutions and values”. Clinton urged the electorate to “vote against radicalism, bigotry, and corruption” and support “fantastic candidates all over the country – including a historic number of women”.