The intervention comes after Jeb Bush attacked Trump not on what Krugman dubbed his "absurd and vicious" immigration policies, but "precisely the issues on which Mr. Trump happens to be right."
Trump is yet to announce an official policy on taxation but he recently told Bloomberg he'd be "okay with" raising taxes for the richest members of society.
The left-leaning economist went on to say President Obama's economic policies - which defy conservative orthodoxy - have so far benefited the economy.
"I’m not saying everything is great in the US economy, because it isn’t ... but the economy has nonetheless done far better than should have been possible if conservative orthodoxy had any truth to it. And now Mr. Trump is being accused of heresy for not accepting that failed orthodoxy?" he asked.
At the same time, Krugman was clear that he isn't endorsing Trump as a presidential candidate.
"I'm not making a case for Mr. Trump. There are lots of other politicians out there who also refuse to buy into right-wing economic nonsense, but who do so without proposing to scour the countryside in search of immigrants to deport, or to rip up our international economic agreements and start a trade war," he wrote.
"The point, however, is that none of these reasonable politicians is seeking the Republican presidential nomination."