Donald Trump has pulled off one of the greatest feats in modern American political history

He was regarded as a joke when he announced for the Presidency. The Saturday night late-night comics had a field day.

Who's laughing now? You guessed it. Donald Trump is relishing this moment.

He has just passed, according to Associated Press calculations, the magic number of 1,237 delegates that ensures he becomes the Republican Party nominee.

That is even before we get to the California vote next month, when the most populous state in the Union has its say.

So, for just a moment, let's marvel at the scale of the achievement.

By winning the nomination of one of America's two major parties - having done so with zero political experience - Donald Trump has already pulled off one of the greatest feats in modern American political history.

The last president never to have held political office was Dwight Eisenhower in the 1950s.

And he, after all, had been Supreme Commander of Allied Forces in World War Two, and so was vastly experienced in leadership terms.

If Trump makes it to the Oval Office, he will be one of the least qualified Presidents in American history.

We had better get ready for the next 166 days - for this will be a brutal, gruelling, relentlessly negative, vastly expensive campaign for the White House.

And if at the end of this marathon Trump actually wins, well, that will truly be one for the history books.