If you follow Krugman, you'd observe the difference in his opinions on Obama debt and Bush/Trump debt surround the real-world events of economic recovery. Krugman often argues for Keynesian economics[1], in that you should drive up deficits in times of economic hardship, and drive them down in times of economic prosperity.
There were a lot of people who disagreed with the Quantitative Easing, specially some of our trading partners.
It seems to have worked for us, but there is Japan who took QE to new heights but to little avail --unless we are to think they'd be even more middling had they not QEd things.
That's a completely different topic of argument. _You_ may not agree with Keynesian economics, and may have examples to cite for your reasoning, but it doesn't speak to Krugman's consistency.
Additionally, QE was only a piece of the recovery. Keynesian economics also advocates for direct investment in infrastructure and other government spending to get people working and money moving.
[1]https://en.wikipedia.org/wiki/Keynesian_economics