Your chart shows the number to be below 5 million until Democrats took control of both houses of Congress. Not sure what that has to do with Bush. But hey, I don't expect Obama supporters to understand actual causal reasoning. Instead, I get the same post hoc garbage liberals have been using for decades.
But since you want to focus on Obama here, let's take a closer look at YOUR stats:
Jan 2009 - Part time employment = 26.9 million
Jan 2015 - Part time employment = 26.6 million
Is that what you call 'gentle decline'?
You're dense, if you're talking about Obama supporters". No wonder the numbers go over your head.
The line to look at is the part-time employment for economic reasons...that is, those who can't find full-time work. It was 4.3 million at the beginning of 2006. By the time Bush left office, it was up to more than 8 million!
By 2016, it was back down to about 6 million...a quarter less than when Obama took office.
Maybe you're not dense...maybe you just hate American workers, and applaud them being forced into part-time jobs.