WASHINGTON, March 8, 2024 (BSS/AFP) - US President Joe Biden will use his State of the Union address Thursday to attack election rival Donald Trump for plotting "revenge and retribution" while offering skeptical voters his own vision of an American comeback.

In one of the most important speeches of his long political career, the 81-year-old Democrat will try to ease concerns about his age by painting himself as the only alternative to an anti-democratic Trump in November's election.

But in a sign of the multiple challenges facing Biden, protesters against his support for Israel's war on Hamas blocked a possible route for his motorcade to the Capitol shortly before the address.

Biden did not mention Trump's name in excerpts released by the White House but took a clear dig at the 77-year-old Republican, who has refused to accept his 2020 election defeat and now narrowly leads Biden in the polls.

"My lifetime has taught me to embrace freedom and democracy," Biden was to say in the primetime speech starting at 9:00 pm (0200 GMT).

"Now some other people my age, see a different story: an American story of resentment, revenge, and retribution. That's not me."

Biden routinely paints Trump -- who was impeached twice and faces multiple criminal indictments including over the January 2021 assault on the Capitol -- as a threat to the survival of US democracy.

- 'Greatest comeback' -

In his speech, Biden was to slam Republican abortion opponents, saying they have "no clue about the power of women in America," in what Democrats see as a key vote-winning issue.

With many Americans struggling from high prices, Biden was to say of the US economy that "in thousands of cities and towns the American people are writing the greatest comeback story never told."

Biden was also set to use the annual speech on the floor of Congress to overcome doubts about the wars in Gaza and Ukraine.

He was to announce during the speech that he has ordered the US military to set up a port on Gaza's coast to bring in more aid, reflecting the acute political pressure from many in his own party.

However dozens of protesters calling for a ceasefire blocked Pennsylvania Avenue, the broad boulevard leading from the White House to the Capitol, an AFP reporter said.

They chanted slogans including "State of the Union is genocide!".

Ahead of the speech, Trump accused Biden of "horrific devastation" during his three years so far in office, focusing on the record numbers of migrants crossing the Mexican border.

"It's time to tell Crooked Joe Biden -- you're fired," Trump said in a video "prebuttal", using the catchphrase of his former TV reality show "The Apprentice."

- Age concerns -

For the millions of Americans tuning in to the spectacle, much of the interest will be not just what Biden says in the joint session of Congress, but how he says it.

Will he stumble, for example? Or will he mix up the names of people and countries, deepening concerns fueled by a recent special counsel report that described him as elderly and forgetful?

The White House said Biden was fully prepared for the speech -- and ready for any repeat of last year's heckling by Trump allies, which he successfully parried with spirited ripostes.

One of last year's hecklers, hardline rightwinger Marjorie Taylor Greene, sported a t-shirt referring to the murder of Georgia student Laken Riley by a suspected migrant.

In line with tradition, First Lady Jill Biden will host a number of guests chosen to highlight the White House's priorities.

This year they include a Texan woman forced to leave the state for an abortion, a woman whose IVF treatment was halted by an Alabama court ruling, and the prime minister of Sweden, which became NATO newest member on Thursday.

The speech comes two days after Trump and Biden all-but set up a rematch of the 2020 election with their sweeping wins in this week's "Super Tuesday" primaries -- but it is a sequel that polls show many US voters do not actually want.