Sometimes a child is able to drag a parent into doing something the parent might not really want to do—say, taking the kid to an amusement park—through a two-step process. The first step is to nag, repeatedly and insistently, about going to the park. The parent, not wanting to be bothered about such a chore, tries to buy time and assuage the child by saying that they aren't going to the park now but they will when a suitable day arises. After some time goes by and the trip to the amusement park still has not been taken, the child's theme becomes, “But you promised.” The issue is framed no longer just in terms of the pros and cons of going to the amusement park but also in terms of the parent's credibility. The parent, worried about maintaining credibility of both promises and threats on other possible matters, gives in.
A similar process is occurring with some of those who, for whatever ill-conceived reason, would welcome a war with Iran. With some of the same people, it is occurring also with the nearer-term issue of intervening in the civil war in Syria. In each case step one is agitation in favor of threatening the use of military force. Step two is to argue that unless the threat is carried out, U.S. credibility will be damaged. Similar to the child who wants to go to the amusement park, the same persons whose urgings led us to get into an option-reducing box then yammer about the damage that results from being in that box, unless we get out of it in the particular way they want.
On Iran, it is hard to know exactly how President Obama, in his innermost thoughts, views the nuclear activities of the Islamic Republic of Iran. It is a fair guess that he does not subscribe to the repeatedly expressed notion that those activities constitute the Greatest Threat to Mankind in Our Time. He clearly does not want a war with Iran. But he is faced with repeated, insistent nagging about this from the government of Israel, and thus from those in the United States who support that government, and thus with all of the U.S. political implications that implies. Not wanting to have his presidency completely sidelined by such things, he tries to buy time and assuage the naggers by saying that an Iranian nuclear weapon would be unacceptable and that all options are on the table to prevent that eventuality. His statements are already fodder for lots of warnings about how badly U.S. credibility supposedly would be harmed if he does not make good on the promise he seems to have made. Some of the loudest voices in making those warnings are those whose pestering pressured him into making the promise in the first place.