Why is this legal in some countries? It seems like a recipe for bribery.

Trump was something like 200/1 to win the Republican nomination. Imagine if you got a group of 100 wealthy people who all bet $100,000 (possible reward of $20 million) on him winning the Republican nomination. Then each of those wealthy people go into poor white trailer park areas and bribe everybody $10 to vote for Trump.

And, all a wealthy American has to do to bet on the election is briefly travel to the UK and set up a betfair and bet365 account.

I am even more intrigued about the fact that the UK doesn't even outlaw betting on UK elections.