Washington DC - President Donald Trump will try to sell voters on the economy during his State of the Union address Tuesday, despite suffering a series of stinging blows ahead of crucial midterm elections this year.

After a breakneck first year back in power, Trump is suffering from low approval ratings while the Supreme Court last week struck down the global tariffs at the heart of the Republican's economic agenda.

But Trump will declare to Congress that America is "strong, prosperous, and respected" as it prepares to celebrate its 250th anniversary, White House Press Secretary Karoline Leavitt said.

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Trump will "proudly tout his administration's many record-breaking accomplishments" and lay out an "ambitious agenda to continue bringing the American Dream back for working people," she added.

The 79-year-old president himself warned on Monday that the first official State of the Union of his second term was "going to be a long speech because we have so much to talk about."

The world will meanwhile be watching for hints from Trump about possible military action against Iran, with a huge US military build-up pressing Tehran to make a deal on its nuclear program.

US media reported that Trump would devote part of the speech to foreign policy, insisting on what his administration calls a "peace through strength" strategy following a series of violent military interventions, including in Venezuela.

Secretary of State Marco Rubio was due to brief House and Senate leaders at the White House ahead of the speech.

Democrats are lining up responses including boycotts and silent protests for the address – mandated by the Constitution, which says that the president shall "from time to time give to the Congress information of the State of the Union."

Adding to the interest will be the guests that both Republicans and Democrats bring to watch the address from the gallery, part of a long tradition.

Trump has invited the US men's ice hockey team after they won Olympic gold.

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But the women's team, who also won gold, said they were declining Trump's invitation after he mocked them in a phone call with the men's team, complaining that he had to invite the ladies or he would "probably" be impeached.

The president was also inviting Erika Kirk, the widow of assassinated right-wing commentator Charlie Kirk, and a trans teen whose mother sued a high school over claims officials hid the fact that the child was transitioning.

Two Democratic members of the House of Representatives said they were bringing as guests the family members of a victim of disgraced late financier Jeffrey Epstein.

Trump, who has been named over 38,000 times in government files on Epstein, denies any links to the sex offender, but the scandal continues to nag at his presidency.