The Obama administration has already halted the transfer of Guantanamo detainees to Yemen, where the failed Christmas Day plot was hatched. But Graham and McCain have called for a wider halt of transfers to include Afghanistan, Iraq, Saudi Arabia and other countries.
Democrats, meanwhile, could ask Mueller questions that have nothing to do with the attempted Christmas Day attack. He helmed the FBI during the Bush administration when, after 9/11, phantom terror threats were used to illegally gather phone records.
Beyond finger-pointing, Congress must consider this month a long-stalled renewal of expired parts of the Patriot Act, the 2001 law that gave law enforcement and intelligence communities new tools to combat terror threats.
The hearings will not end today, either. The Homeland Security Committee, chaired by Sen. Joe Lieberman, the Connecticut independent, will hear testimony Thursday on the Fort Hood attack in November, when Army Maj. Nidal Hasan allegedly killed 13 on the Texas Army installation.
An independent review recommended new security procedures, background checks and changes in policy regarding what is kept in a servicemember's personnel file.
Lieberman has criticized the report, which he said should have been more focused on the threat of Islamic extremism.
"I believe firmly that if [the Defense Department] educates its personnel about violent Islamist extremism -- and how terrorists distort the Islamic faith to promote violence -- we will increase trust between the thousands of Muslim-Americans serving honorably in the military and their colleagues," Lieberman said in a statement Jan. 15.
The Associated Press contributed to this report.