THE voters were having their say on Tuesday as Donald Trump faced the first US national election of his presidency against a Democratic party hoping to turn the page on a stunning defeat in 2016.

Pollsters, who largely failed to predict Trump’s victory over Hillary Clinton two years ago, were more reluctant to commit themselves ahead of the midterms in which the presidency is not up for grabs but the shape of federal and state government is.

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Trump, the Republican party’s chief messenger, warned that significant Democratic victories would trigger devastating consequences.

“If the radical Democrats take power they will take a wrecking ball to our economy and our future,” Trump declared in Cleveland, using the same heated rhetoric that has defined much of his presidency.

He added: “The Democrat agenda is a socialist nightmare.”

Democrats, whose very relevance in the Trump era depended on winning at least one chamber of Congress, were laser-focused on health care as they predicted victories that would break up the Republican monopoly in Washington and state governments.

“They’ve had two years to find out what it’s like to have an unhinged person in the White House,” said Washington governor Jay Inslee, who leads the Democratic Governors Association. “It’s an awakening of the Democratic Party.”

Democrats could derail Trump’s legislative agenda for the next two years should they win control of the House or the Senate.

Perhaps more importantly, they would claim subpoena power to investigate Trump’s personal and professional shortcomings.

Some Democrats have already vowed to force the release of his tax returns.

Others have pledged to pursue impeachment, although removal from office is unlikely so long as the Republicans control the Senate or even maintain a healthy minority.

The Democrats’ fate depends upon a delicate coalition of infrequent voters, particularly young people and minorities, who traditionally shun midterm elections.

If ever there was an off-year election for younger voters to break tradition, this is it.

Young voters promised to vote in record numbers as they waged mass protests in the wake of the February mass shooting at a Parkland, Florida, high school that left 17 students and staff dead.

Democrats are drawing strength from women and college-educated voters in general, who swung decidedly against Trump since his election.

Polling suggests the Republican coalition is increasingly older, whiter, more male and less likely to have a college degree.

Democrats boast record diversity on the ballot.