In the olden days we in Britain used to vote for constituency MPs, each one appointed to serve his local community; who would then coalesce into parties, with the largest of them – or largest coalition – forming a government, and with a leader chosen from among them. The leader would become ‘prime minister’, and select his other ministers, formed into a cabinet, to govern the country collectively. Later on the parties were formalised, which meant that their leaders were known beforehand. That was the order of things in Britain. It was how it had been done for centuries, even under monarchical rule. When monarchical rule ended, it was by keeping the king or queen as a mere figurehead but reducing his or her powers, and elevating parliament above him (or her). That’s what ‘parliamentary democracy’ means.
It was totally different from the way the monarch was got rid of over on the other side of the pond. In the newly-independent USA s/he was replaced with a President, with similar powers to the old King, with the crucial difference that he (always a man, up to now) was elected directly, and side-by-side with the other arms of government. That’s what the American President is today: an elected King. The USA has not really moved on from the 18th century.
This explains the differences between our two electoral systems, with the British supposedly voting for a local MP first, and a party second, and the Prime Minister emerging out of that process; whereas in America the head of state is elected directly, side-by-side with Congressmen/women and the like. That’s why the American system turns so much on the personalities of the rival candidates. In Britain it shouldn’t do; but for years commentators have been noting how ‘presidential’ we have become.
That’s a pity. If we had been presidential in 1945, we would have got Churchill rather than Attlee, and so (probably) no welfare state. If America were parliamentary today, it certainly wouldn’t have been landed with Trump, or not for long. And if Britain were truer to her old ‘parliamentary’ traditions today, Corbyn would undoubtedly stand a better chance in the coming general election, and May probably none.