The United States marked a politically-charged 250th anniversary on Saturday as President Donald Trump exerted his influence over the usually non-partisan celebrations.

His speech, described by some analysts as rally-like, included soaring rhetoric on American exceptionalism and warnings about the threat of communism.

Dangerous, record-shattering weather in Washington and the lightning strikes in the distance prompted a two-hour evacuation of the National Mall ahead of his planned speech.

Nearly every other aspect of the celebration bore Trump’s imprint., as decisions he made transformed an official commemoration into another polarising moment in American politics.

He hailed the United States as the "crowning achievement" of human history, even as he used the event to renew his attack on domestic opponents he branded communists.