But officials concede the difficulties of targeting within the city are considerable.
Others in his side were readier to concede the difficulties in upholding this part of the law.
Everyone who fights spam concedes the difficulty of outsmarting the generators.
Mr. Wolfowitz conceded the difficulty of drafting a Pentagon budget while the military strategy remained a subject of intense debate.
Diners can be seen corralling votive candles to read the menu, and some restaurants have conceded the difficulty.
He also said the F.B.I. had properly handled the information it received from Russian intelligence agencies about the older of the two suspects, Tamerlan Tsarnaev, even as Mr. Obama conceded the difficulty of preventing attacks.
Last month, Mr. Annan conceded the difficulty of filling the job because of its dangers, saying that several candidates who had been interested in taking it had later withdrawn, citing family objections.
His mourners, while conceding the difficulty of plumbing the nature of hatred and homicide, demanded a full investigation and disputed official insistence that neither racism nor homophobia had been a motive.
He has reopened neighborhood police stations and developed a plan to eliminate a $300 million budget gap, but he concedes the difficulty of reviving a city with pervasive poverty and unemployment.
"The first order of business will be the development of our business model," says Masters, even as he concedes the difficulty of that enterprise.
