What's the meaning of "put someone on one's heels"?

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What's the angle, five words?

Far left of center.

That's four.

Very far left of center.

Enough to put Walker on his heels?

f*ck his heels.

This will put him on his ass.

from season 1 episode 1, House of Cards

What's the meaning of "put someone on one's heels"?

'To put someone on their heels' is a variation on 'rock someone back on their heels'.

From the Oxford online Dictionary site (http://www.oxforddictionaries.com/definition/english/set-or-rock-someone-back-on-their-heels):

set (or rock) someone back on their heels
Definition of set or rock someone back on their heels in English:
Astonish or disconcert someone:
'She said something that rocked me back on my heels'. 'Then, just as the team seemed to be establishing a foothold, two interceptions set them back on their heels'. 'A tremendous drive set them back on their heels, forcing them to concede a penalty.' 'They counter attack from deep in their own defence and our forwards should have been tackling them with a ferocity that would have disrupted them and rocked them back on their heels near their own lines.'

Essentially it describes a physical shock that almost knocks someone backward, but they manage to retain their balance while pivoting on the heels of their shoes. The next stage would be, 'To knock someone on their back (or whatever local expression applies to buttocks).'

According to dictionary.com, to set someone on their heels is to put them in:

Surprise, shock, or disconcert, as in The news of their divorce set us back on our heels. This idiom, with its graphic image of someone being pushed back, dates from the first half of the 1900s.