American Presidents don't do things by half.

They bring with them the longest convoys, the biggest aeroplanes and the largest travelling media packs.

But here in London today, Barack Obama decided he would almost bring a pretty big bomb and detonate it in the middle of the Leave campaign.

He could have tiptoed around the big questions about the EU referendum.

He could have chosen his words more cautiously.

But he didn't.

I asked him why he thinks he got a right to intervene in our domestic debate and in his response, he didn't beat about the bush.

We're a friend, he said, and while I am not casting a vote myself, "I'm offering my opinion."

The British people should be afraid of hearing an argument being made, he went on adding, "that is not a threat."

And he demolished the claim from the Leave campaign that outside the EU the UK would be able to do more trade with the US.

"I figured you might wanna hear from the President of the United States", he said.

A trade deal between the UK and the US isn't going to happen anytime soon, said Mr Obama, because the US will want to concentrate on a bigger market: the European one.

And devastatingly he added, the UK will be "at the back of the queue."

Given there are millions of jobs at stake if the UK left the EU, if I had to vote he said, "that's not something I'd probably do."

Answering the accusation about his right to enter this debate, a point frequently made by Leave campaigners, the US President said a UK Leave vote could destabilise Europe, which he said was the US's largest trading bloc.

"That's gonna affect the US," he said.

There was a small note of comfort for the Leave campaign here.

Mr Obama said the oft-referred to "special relationship" between the UK and US would not be affected if we voted to quit the EU.

But at the end of the first official week in this campaign, you do have to chalk it up to Remain.

And Downing Street knows it.

Chris Ship, ITV deputy political editor