WATCH LIVE: President Trump delivers his first State of the Union address
President Donald Trump (AFP/File / Fabrice COFFRINI)

Embattled US President Donald Trump delivers his biggest speech of the year Tuesday, a State of the Union address designed to sell his economic record to a skeptical and fiercely divided America.

Trump's speech is scheduled to begin at 9:10 p.m. ET. Watch live streaming video below:

Trump's maiden address to the country -- last year, he delivered a primetime speech that was technically only to Congress -- presents a once-in-a-year opportunity for the president to mend his sunken approval ratings.

As many as 40 million are expected to tune in when he takes to the floor of the House of Representatives just after 9:00 pm (0200 GMT).

"It's a big speech, an important speech," Trump said Monday, teasing his remarks.

Over the years, the event has lost some of its influence, but it can shape public debate for weeks to come.

In 94 previous addresses, presidents have described the state of the union as "good," "strong," "sound" or in the case of a glum Gerald Ford, "not good."

Expect no such moderation from the 71-year-old real estate mogul and reality TV star.

The state of the union is "incredible," said White House spokeswoman Sarah Sanders, outlining a speech that will be long on claims of achievement.

Trump is expected to tout a long bull run on Wall Street and improving growth rates, something the White House is calling a "Trump bump" linked directly to the recent "Trump tax cut."

That narrative suffered a setback when stocks tumbled at the opening Tuesday, amid fears of a bubble. But expect Trump to plow on.

"We worked on it hard, covered a lot of territory," Trump said of the speech, "including our great success with the markets and with the tax cut."

Since Trump came to office a year ago, the Dow Jones Industrial Average is up by around 33 percent. The unemployment rate is at a 17-year low.

Trump recently told global business leaders in Davos, Switzerland that "America is open for business" again.

During his first year, Trump has often sought credit, but he has appeared less concerned about widening his appeal -- defying norms and sticking to a base-first approach.

With legislative elections scheduled for November and the probe into his campaign's ties with Russia intensifying, Tuesday's speech may see something of a change in strategy.

"This is a president who wants to lead for everybody," said Sanders. "He's not looking to lead for any one person, any one group, but he wants to be the president of the United States."

Trump's approval rating is languishing around 40 percent, according to the RealClearPolitics average, and opposition to his presidency is fierce.

At a donor retreat in California this week, Republican strategists warned that an unpopular president and strong enthusiasm among Democrats could spell doom.

Adding to Republican woes is a steady stream of revelations about the Trump campaign's ties to Russia, which is accused of trying to tilt the 2016 election in Trump's favor.

The eve of Trump's remarks were dominated by the departure of a key figure in that probe, the deputy head of the FBI, who had come under sustained public criticism from the president.

The White House also faced criticism for slow-walking lawmakers' demands for sanctions against Russia.

- 'America First' -

Tuesday's speech is also expected to touch on the highly charged issue of migration, where Trump continues to play firmly to his base.

Two couples whose daughters were murdered by MS-13, a Salvadoran gang, are among those the White House invited to attend the address in Washington.

His remarks are being crafted in part by aide Stephen Miller, who is known in Washington as a hardliner on immigration and has been pressing for an uncompromising stance.

"For many, many years, they've been talking immigration, they never got anything done. We're going to get something done, we hope," Trump said.

Trump can also be expected to lift his gaze beyond the United States to what Washington sees as Iran's troublesome activities across the Middle East, as well as North Korea's nuclear and ballistic missile programs.

And trade is expected to be a strong focus, with Trump repeating claims that the current terms of global business are unfair to the world's largest economy.

"The world has taken advantage of us on trade for many years, and as you probably noticed we're stopping that, and we're stopping it cold," Trump said.

- The opposition -

The Democrats' official rebuttal will come from up-and-coming congressman Joe Kennedy of Massachusetts, but 2016 White House hopeful Bernie Sanders and others will also offer their takes.

They are likely to concede that the economy is growing, but perhaps not for everyone.

"Trump inherited a years-long economic recovery but has yet to turn it to the advantage of working Americans," said analysts at the left-leaning Center for American Progress.