He's not defending Bush's spending (I don't think anyone outside the administration would try and defend Bush's spending); he's just pointing out that Clinton would have spent more than he did if he'd had a Democrat congress.
On top of that, the American people aren't blind to the overspending. Republicans not being fiscally conservative (along with a few immoral Republicans getting conveniently-timed major press coverage) is what lost the GOP control of Congress two years ago.