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The cars, the flags, the phalanx of security guards in shades, the size of the entourage, the easy cool of the president himself and the White House hoopla will dominate Westminster on Friday.

As one source admitted to me it's a "bit pathetic", but Westminster types are, as ever, beside themselves with excitement as the leader of the free world rolls into town.

This visit is different though, not just because it's Obama's farewell tour but because he is here to intervene in our politics too.

As he'll argue, the United States wants us all to choose to stay in the EU. That much has been known for some time. He won't hold back either, and .

What is less clear is whether the president's intervention will actually make very much difference in the referendum. Downing Street clearly believes it will, and is determined to make as much as they can of the visit, and the White House's support for their position.

Who can blame them? In the current battle over our place in the European Union the political logic is clear. Why wouldn't you want the leader of the free world on your side and maximise the potential gain by holding not just political meetings, but a major press conference and a public visit over the weekend with happy, smiling, young voters?

One pollster tells me politicians here would kill for the kind of respect and approval that President Obama has among British voters, despite his difficulties at home in the US.

And of course, a significant proportion, maybe more than 20% of voters are yet to make up their minds on the referendum. But will President Obama's support shift many of them into the Remain column?

Not necessarily. Senior sources in the Remain camp suggest that, rather than relying on the intervention of one politician, however senior, Obama is contributing to the 'weight of credibility' they are trying to build.

They believe in recent days comments from organisations like the IMF, Nato, the unions, American Treasury secretaries, have created a momentum, and an authority that has the "Outers" firmly onto the back foot.

Obama, the thinking goes, could knock them even further off balance.

Even the most dedicated Brexiteer would be kidding you if they suggested they wouldn't like endorsements like this.

But beyond making public accusations of hypocrisy, there isn't much that they can do, and perhaps they shouldn't bother.

Sources in the Out campaign suggest that although Obama's backing could be a useful motivator for the Remain camp, it's part of the roll out of big names that they had always expected.

For months Downing Street's hoped-for "grid" has been pretty clear - FTSE bosses, then the Bank of England, then the IMF, then Obama, the grand finale.

Indeed, some "Outers" believe their best chance of winning is to present the referendum as David v Goliath, the plucky outsiders versus not just the British, but the world's establishment, (remember Boris Johnson even alluded to the CIA in our interview with us last week).

So, even if some of their backers would like the campaign to be more aggressive in putting forward their "endorsers", the truth is, they can't be matched, so strategically, maybe the better judgement for them is to maximise the distinction.

Forget "if you can't beat 'em, join 'em". If you can't beat 'em, show how different you are.