>>> everything. "nightly news" begins now.

>>> good evening. the next moving pieces on syria appear to be in place tonight and the story changed again today after the american people witnessed a rare event last night -- a primetime address to the nation by the president that wasn't what he intended to say originally. it was originally designed to make his case to attack syria for using chemical weapons . that appears to be on hold. so is the vote in congress. now we see in if diplomacy works while the president is making it clear he believes the use of chemical weapons cannot stand, the question tonight is how to secure them all. prior to departing with secretary of state john kerry for talks in geneva, our chief foreign the affairs correspondent andrea mitchell starts us off tonight.

>> reporter: tough words from the president.

>> let me make something clear. the united states military doesn't do pinpricks.

>> reporter: unusual for a presidential address to the nation, no call for action.

>> i have asked the leaders of congress to postpone a vote to authorize the use of force while we pursue this diplomatic path.

>> reporter: vladimir putin 's proposal to put syria 's chemical weapons under international control and destroy them. but even if an agreement is reached at the u.n., can it work? the syrian chemical arsenal is scattered. this satellite shows a suspected depot, bunkers ring the periphery.

>> it is a war zone at the moment. a very bitter, difficult civil war is happening. to do this sort of thing of destroying chemical weapons in place is going to be hugely difficult.

>> reporter: the president is sending secretary of state john kerry to geneva tonight to test whether russia is serious.

>> this cannot oh be a process of delay, of avoidance. it has to be real.

>> reporter: what's in it for putin ? protect ing russia's naval base in syrian territory. keeping the chemical weapons away from islamic terrorists in place s like chechnya. keeping assad in power. critics say the president's zig zags have given the u.s. a weak hand.

>> i think we'll have a crippled negotiating team walking into the room where putin holds the cards on getting rid of chemical weapons .

>> reporter: putin is already flexing muscles at the u.n. where security council members met after a blocked resolution supported by the u.s., france and great britain to preserve the military option if the assad regime doesn't comply. and there is the challenge at home. most americans like these of the skokie, illinois, public library want to avoid military action .

>> we continue have these wars, another war after another.

>> we need to spend the money in the united states and forget the middle east .

>> i don't want to hear emotional arguments. i think it is to manipulate us.

>> reporter: the question the president has not answered, what will he do if diplomacy fails? andrea mitchell , nbc news, washington.