We don't yet know how many House seats the Democrats will lose next Tuesday, but it could be a lot. The Post's Election Lab tool figures a modest switch, with the GOP waking up on Wednesday holding 242 seats. (The GOP controls 233 seats currently.)
And if that's the case, Obama doesn't pass Truman. In fact, if that's the case, Obama would only be in eighth place since the post-Civil-War transition to a Democrat-vs.-Republican polarization. Here's the net number of House seats lost by each president in any midterm during his tenure, going back to Ulysses Grant.
(Note that our figure, based on data from the House historian, differs slightly from Rothenberg's.)
Obama has a way to go to catch Truman. And he's got much further to go to catch FDR (who of course had far more midterms). But the grand champion of midterm losses was Grover Cleveland, who got smacked around in midterms on two non-consecutive occasions. What's more, that happened when the House was much smaller, meaning that the effect of losing so many seats was heightened.
If you exclude the election when each president won (during which, to be fair, they didn't have much affect on policy), Obama does slightly better, thanks to the clawback in 2012. Under that standard, Teddy Roosevelt does much better, being the only president to actually get above water.
The point here isn't to make Obama's record on House races seem un-terrible; that's impossible. Instead it's to point out that a) having very few presidents makes "going back 100 years of presidents" a somewhat softer comparison and that b) politics in the late 1800s must have been completely amazing.