In 2009 and again in 2011, congress passed laws blocking the transfer of prisoners from the Guantanamo Bay detention facility. They were part of omnibus spending bills, so refusing to sign them would have been a disaster. I don't know what you expected Obama to do, short of declaring himself emperor and ruling by decree.
Actually no, congress didn't outright block the transfer of prisoners from Guantanamo. They simply imposed conditions (admittedly excessive ones) that needed to be met before the transfer could be made (unless I missed something). From the bill (section 9011) I know of we have:
(d) The President shall submit to Congress, in classified form, a plan regarding the proposed disposition of any individual covered by subsection (c) who is detained as of June 24, 2009. Such plan shall include, at a minimum, each of the following for each such individual:
(1) A determination of the risk that the individual might instigate an act of terrorism within the continental United States, Alaska, Hawaii, the District of Columbia, or the United States territories if the individual were so transferred.
(2) A determination of the risk that the individual might advocate, coerce, or incite violent extremism, ideologically motivated criminal activity, or acts of terrorism, among inmate populations at incarceration facilities within the continental United States, Alaska, Hawaii, the District of Columbia, or the United States territories if the individual were transferred to such a facility.
(3) The costs associated with transferring the individual in question.
(4) The legal rationale and associated court demands for transfer.
(5) A plan for mitigation of any risks described in paragraphs (1), (2), and (7).
(6) A copy of a notification to the Governor of the State to which the individual will be transferred, to the Mayor of the District of Columbia if the individual will be transferred to the District of Columbia, or to any United States territories with a certification by the Attorney General of the United States in classified form at least 14 days prior to such transfer (together with supporting documentation and justification) that the individual poses little or no security risk to the United States.
(7) An assessment of any risk to the national security of the United States or its citizens, including members of the Armed Services of the United States, that is posed by such transfer and the actions taken to mitigate such risk.
Yes, it's a lot of paper work (there's further notifications required 15 days prior to moving) but none of it is impossible. Also note, at no point does it require further approval of congress. Once the paperwork is submitted the President is good to go. Now admittedly, if he did try this congress would likely try to introduce a new bill blocking it (thus the 45 day notice) but hey, he could veto that one specifically unless overruled by congress in which case it really isn't his fault anymore. But he hasn't. The only thing stopping him at this point is paperwork. No law or specific prohibition from congress is doing it. And that is the disgraceful part of it.