United States President Donald Trump has claimed that America’s identity is facing a renewed attack as the country prepares to celebrate its 250th Independence Day.

Speaking at Mount Rushmore on Friday, Trump praised the nation’s history and achievements but argued that its values and traditions were being challenged by what he described as radicals, extremists and a resurgence of communist ideology.

He said there had been attempts in recent years to change America’s character, weaken its patriotic spirit and distance citizens from their history. Trump also stressed that while people do not have to be born in the United States to be American, they should embrace and appreciate the country’s values and achievements.

The remarks come as progressive Democrats have recorded gains in recent primary elections ahead of the November midterm polls. Trump has repeatedly warned that the rise of the political left poses a major threat to the country.

The president’s speech formed part of events marking America’s 250th anniversary. He is expected to headline July 4 celebrations in Washington with a campaign-style rally, military flyovers and a major fireworks display.

The anniversary, however, comes at a time of deep political division. Trump has faced criticism over his handling of immigration, the economy and executive powers, while some celebrations linked to the milestone have drawn lower-than-expected attendance and criticism over their political nature.

A recent poll by Quinnipiac University found that 61 per cent of Americans believe the country is not fully living up to the ideals set out in the Declaration of Independence, although opinions remain sharply divided along party lines.