The OP is not flying to the US but arriving at IST from the US; a totally different situation in terms of security (however, it may be that additional security is applied for TLV flights - I don't know).
Anyway, 55 min is more than enough for this transfer, which will be very easy. Just follow the transfer signs, show your onward BP (or if you didn't get it at IAD, obtain a BP from the TK transfer desk on arrivals level) and take the escalators one level up; you will then be in the transit/departure hall. It is very very easy; no need to to worrry.
You will not pass customs or immigration for this transfer.
Security checks take place at the departure gates. I have passed IST many times and I have never experienced security checks to be "chaos" or time consuming. No need to worry about this.