(CNN) Michael Bloomberg has spent more than $350 million of his own money on advertising in support of his 2020 presidential campaign. But President Donald Trump's now near-constant attacks on the former New York City mayor have given Bloomberg something no amount of money can buy: a growing sense that the incumbent is very, very worried about him.

Within 10 minutes on Thursday morning, Trump had sent out two tweets attacking Bloomberg for, among other things, his short stature and being a "mass of dead energy." Two days earlier, Trump had tweeted this about Bloomberg: "Mini Mike is a short ball (very) hitter. Tiny club head speed."

In the 13 days of February to date, Trump has sent at least eight tweets attacking Bloomberg, according to the invaluable Trump Twitter Archive . That represents a significant ramping-up of Bloomberg-dedicated tweets from Trump and far more than Trump has targeted anyone else in the Democratic field over that period of time.

Which is important! Because anyone who has followed Trump's campaign and presidency understands that his Twitter feed is the best window into what the President is thinking at any given moment. It's like being able to look into his mind and emotions -- constantly. So when Trump fixates on something or, in this case, someone, you know it's meaningful.

And Bloomberg, looking for ways to change the subject from his past support as mayor for the "stop and frisk" policing policy, smartly jumped on Trump's laser-like focus on him. At a campaign rally in North Carolina on Thursday, Bloomberg had this to say about being in the President's crosshairs (bolding is mine):

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