Donald Trump enters this week with renewed momentum after his impressive victory in New York.

But now there is a fresh twist in his roller-coaster campaign for the Republican nomination.

His two rivals, Ted Cruz and John Kasich, are teaming up in a desperate bid to stop Trump. It's a brazen effort to derail the New York billionaire ahead of the Republican convention in July.

Under the agreement that has emerged overnight, Cruz and Kasich will not compete against each other in a state where one is clearly stronger. So, for example, Kasich will let Cruz focus on Indiana, a state which has emerged as crucial to the "Never Trump" movement.

But it may not work. In the eyes of many Republican voters, it will only serve to validate the central Trump narrative that the party elite is conspiring to stop him from winning the prize.

The Trump campaign has responded with a withering tweet:

The Republican Party still looks set for an implosion of epic proportions, possibly splintering the conservative movement in America for years to come.

If the party accepts Trump as its nominee, it has been hijacked by a bigot and a political maverick.

If it manages to derail his bid, even though Trump has won more votes and delegates (by far), the party looks corrupt and broken, a tool in the hands of the Establishment.

This is a political drama with no happy ending. Except for Hillary Clinton and the Democrats.