"Clotheslining" someone means suddenly holding out your arm across their face or neck as they run past, unsuspecting.

Stiffarming someone means punching them with elbow locked, so there is no possibility of your yielding, which further uses their heedless onward rush into you against them.

What Congress did this Winter to oppose telco amnesty wasn't really a surprise to Bush (though its success might have been). It was a head-on confrontation, not an ambush as Bush rushed attack someone else. And it was notable mainly in its refusal to yield, which let Bush's further attacks beat his own face against the Democrats' fist.

Stiffarm is a more accurate image.