Donald Trump isn't in Chicago but his presence hangs over everything and he is following events here.

A couple of aides told me, a little implausibly, that the former president is not tuning into the Democratic National Convention because he has no interest in watching a Democratic Party "infomercial".

But one senior campaign official confirms, anonymously, that Trump is watching and is irritated by the attacks against him.

In the view of one ally who speaks to the former president every week, Trump wins in November if he sticks to talking about the economy, the border and crime.

At the start of this week, that looked possible. Trump scheduled a string of rallies, in Pennsylvania, Michigan, North Carolina and Arizona - each was themed to focus on exactly those political and economic topics.

But with night after night of anti-Trump speeches here in Chicago, staying on message has gone out the window. And it's not what his supporters tell him they want anyway.

The North Carolina event on Wednesday was vintage Trump - and it became a referendum on his own team's strategy. "They always say, 'Sir, please stick to policy, don't get personal'... and yet [the Democrats are] getting personal all night long, these people. Do I still have to stick to policy?" Trump asked.

Then he polled the crowd: more policy or go personal? His fans roared, they wanted the Trump show, not a list of boring economic proposals.

"My advisers are fired!" he joked. Then he said he'd stick to policy but couldn't let the attacks go unanswered.

So the campaign strategy now seems to be at the whim of the candidate and the feedback of his crowds. That makes life difficult for his campaign advisers who repeatedly tell me their single biggest concern in this election campaign is whether they can keep Trump focused on issues and off the controversial personal attacks.

There have been a couple of those this week already.

Late on Wednesday night, Trump took to social media to criticise the Democratic Pennsylvania Governor Josh Shapiro, who had given a rousing speech earlier in the evening. Trump didn’t like what he heard.

"The highly overrated Jewish Governor of the Great Commonwealth of Pennsylvania, Josh Shapiro, made a really bad and poorly delivered speech," Trump wrote.

"I have done more for Israel than any President…Shapiro has done nothing for Israel, and never will."

The fact that he singled out Mr Shapiro as Jewish has not gone unnoticed. It was picked up on the US morning shows as an example of a racial dog whistle.

After the Obamas criticised Trump at the DNC on Tuesday night, he responded during his rally in North Carolina, and, again, there was a similar racial innuendo.

"Did you see Barack Hussein Obama last night," Trump said. "He was taking shots at your president. And so was Michelle."

They did indeed take pretty personal shots at him, but the use of Mr Obama's middle name has long been used to stoke racial animosity towards him.

The problem for the Trump team is that their candidate thrives on controversy which then dominates headlines, and then distracts from their attempts to point out weaknesses in his opponent's policy positions.

"It doesn't matter what he talks about for 45 minutes," one adviser told me on the condition of anonymity. "One comment or answer to a question gives the left all they need to change the subject."