Great moments in presidential "I'm not [blank]"

I'm NOT WEAK: Obama

I'm NOT WEAK: Obama hits back at foreign policy critics as he vows to ramp up support for Syrian rebels

I would say it's been a truism since at least the early 1970s that if a president has to explicitly deny a meme that has arisen about him, then it's almost certainly true. 

Nixon: "I am not a crook." 

Bill Clinton: "I did not have sex with that woman." 

And now Obama, I am not a weak president

Of course, Nixon's a Clinton's transgressions were both moral and legal, unlike Obama's failures, which are political and programmatic. But they are nonetheless real, and not made less so by his having to deny them.