Boris Johnson is a former editor of this newspaper, and as such has the right to be treated with a courtesy Spectator journalists do not normally extend to politicians who do not enjoy his advantages.

I am therefore writing with the caution of a lawyer and the deference of a palace flunkey when I say that Johnson showed this morning that he is a man without principle or shame. He is a braying charlatan, who lacks the courage even to be an honest bastard, for there is a kind of bastardly integrity in showing the world who you really are, but instead uses the tactics of the coward and the tricks of the fraudster to advance his worthless career.

He might have replied to President Obama's argument that we should stay in the EU with arguments of his own. When Obama said that the EU magnified British influence in the world, Johnson might have shown how our membership diminished us. When Obama said that the EU spread values that had been nurtured in Britain – democracy, the rule of law and open markets – Johnson might have shown how the opposite was the case. When Obama, spoke of the special relationship between Britain and America, Johnson might have reassured doubters by explaining how it would survive Brexit. When Obama implied that the United States was worried sick because only Britain's and the West's enemies want us to leave, Johnson might have given us his thoughts on where we would stand in the world once we were gone.

But to do that would require Johnson to deploy facts British voters could check, and come up with arguments we could test. He would have to, in short, engage in rational debate. Only a fool would believe that he could. True to his recent form, Johnson preferred to imitate Donald Trump.

Johnson lacked the common courtesy to acknowledge that Obama's concerns were genuine if in his view misguided. Instead he sunk into the gutter and stayed there. Obama wanted the British to stay in the EU, he explained to Sun readers, because he hated us. No, really he did, and Johnson could prove it. Obama had manifested his hatred by having a bust of Winston Churchill removed from the Oval Office. Johnson could not bring himself to say that Obama ordered the bust's removal or even knew of it. Instead he made the charge, and then added the sneaky caveat:

“ No one was sure whether the President had himself been involved in the decision.

But why, Sun readers might wonder, would Obama hate Britain and remove Churchill's bust? The President said this very morning that he was in London to talk to David Cameron about helping in the joint fight against Islamic State. This is not on the face of it the action of a politician who means us harm.

Johnson knew better, and slyly attributed base motives to the President:

“ Some said it was a snub to Britain. Some said it was a symbol of the part-Kenyan President’s ancestral dislike of the British empire – of which Churchill had been such a fervent defender.

And with that cowardly sentence, filled with 'some saids' so he could sneak away from its implications, if needed – Johnson abandoned what few rights he possessed to be treated as a decent politician, journalist or man.

Who are the 'some' who say that Obama is a Kenyan at heart? Those 'somes' started as somebodies in the birther movement, which could not accept a black president of the republic. They showed their contempt for democracy by trying to invalidate Obama's election by saying he was not American-born (as the constitution requires). They showed their contempt for truth, when they advanced a claim about Obama's birth that was demonstrably false.

It was a lie, but a convenient lie that many wanted to believe. A 2012 New York Times/CBS News Poll found that 45 percent of Republicans though that Mr. Obama was born in Kenya.

I'm not someone who throws accusations of racism around – it's too serious a charge to devalue. But, come now, the fantasy that Obama is the heir of the Mau-Maus with no right to govern is a racist lie that appeals to deep, dark traditions in the US. From slavery, through the Civil War, the backlash against Reconstruction, and Jim Crow, the argument has been the same: blacks have no right to vote, and black politicians have no right to rule.

Johnson perpetuates the fraud. Obama is not speaking as a friend, Johnson implies, he has been corrupted by the dark, primal anti-British hatreds of his Kenyan ancestry (or so 'some' would say).

There will be much more in this vein from Johnson and the rest of the 'Leave' gang. As I have mentioned before, not one of Britain's allies thinks we should go. The 'leave' crew has no option but to denigrate them all. When the IMF and the Treasury say we will be poorer if we pull out, they must be lying. When as Andrew Neil pointed out, not one reputable study says we will be better off if we vote with Johnson, reputable economists must be damned too.

In these circumstances, Johnson must forget what he learned on the playing fields of Eton and go for the man and not the ball. Smears and conspiracy theories are all he and his friends have.

For 'Leave', everyone in this debate is lying or corrupt or advancing a special interest: everyone, that is, except them.