It's hard to look smart dealing with such abstrusities unless you're truly ready to appear both brilliant and plain-speaking at the same time. Where's Charles Krugman when you need him?
The boldest could do little more than acknowledge, yes, GDP had indeed grown more fastly on his watch, adding meekly that maybe Trump shouldn't get all the credit. Then they clasped their hands on the desk in front of them and waited for the next question (which hopefully wouldn't involve long division).
Trump's GDP numbers are pretty good numbers, no question, but not wildly out of line with what you'd expect from an economy in the later stages of a long-term economic growth spurt.
Since the second quarter of June 2014 the US has enjoyed 20 straight quarters of uninterrupted GDP growth. (This is the second longest recovery on record, someone said.) Numbers even Tom Brady could admire.
Trump characterized his "GDP accomplishment" as an "economic miracle," but even an increase of 100% would at best be only near-miraculous. It happens. More to the point, skeptics might ask, what, or more specifically, where was he actually measuring?
Ignoring for the moment that quarter-to-quarter GDP can be a volatile number and even two years of a presidential term might not be enough time for a legitimate assessment, let's just try to figure out what point of comparison the President had in mind.
GDP growth for 2018 will come in at about 3%, an improvement over any part of Obama's tenure no matter how measured. (2015 GDP grew 2.9%.) But for it to have really doubled, there would need to be some Obama GDP metric of 1.5% or less to compare it to. What would fit that bill and still make for a sensible comparison? What could the President have been thinking?
GDP growth in Obama's last year in office was 1.9%. Hmm, close. Almost 60% better for Trump. But not nearly double. Given GDP's quarter-to-quarter volatility, maybe Trump felt such a narrow-term comparison might smack of cherry-picking anyway.
So perhaps Obama's last two years compared to Trump's first two. That would produce average annual GDP growth of 2.6% for Trump versus 1.96% for Obama. Ooh, that's worse: only 32% better.
Similarly unsatisfactory results come from comparing Trump's two years to Obama's two full terms together or just the whole second term alone. And again, there's the problem of asymmetric comparisons
The thought occurs, given that the Donald probably doesn't know much about GDP beyond how to spell it, maybe he simply took his most recent reported quarterly GDP growth figure (Q3 '18) on hand versus Obama's last quarter in office (4Q '16).
This, of course, is an apples-to-oranges comparison, looking more at quarter-to-quarter volatility than actual growth. (Which is what GDP is designed to do, by the way: spot and annualize current versus historical growth trends.)