Did Donald Trump forget the words to the US national anthem?

Donald Trump has been caught on camera appearing to forget the words to his own country's national anthem.

He was at an American football match on Saturday night between LSU Tigers and Alabama Crimson Tide, when a camera was turned on him during 'The Star-Spangled Banner'.

An audience of close to 20 million viewers got to see the US President singing along to the final lines of the 200-year-old tune's first verse, usually the only one performed at sports matches. 

Well, most of the lines. After "O say does that star-spangled banner yet wave", Trump stayed mum for the first half of the final line - "O'er the land of the free" - before rejoining the rest of the crowd for the second half, "and the home of the brave", coming in noticeably late.

It's not the first time Trump - who has in the past said people who disrespect the anthem shouldn't be in the US to begin with - appears to have forgotten a line from the song, which was officially made the US anthem in 1931.

In January last year he was seen mouthing some words and leaving others out during a college football game in Atlanta. 

The latest clip triggered mockery from opponents on social media, some of whom accused Trump of not knowing the words to the anthem at all. This would appear to be untrue however, with other videos showing the President - who has used nationalist slogans and imagery to curry support - singing the anthem without a hitch. 

Video retweeted by Trump shows he was cheered at the LSU-Alabama game, after being booed at a baseball match and an MMA fight in recent weeks. The game was held in Alabama, a solidly Republican state, which UK paper The Independent labelled a "safe space" for the notoriously combative President.