Updated at 1:15 p.m. ET
In the wake of Osama bin Laden's death at a large complex not far from Pakistan's capital city, congressional leaders are putting new scrutiny on the United States' relationship with Pakistan.
The U.S. has a delicate alliance with Pakistan. The nuclear-armed nation is a critical partner in the United States' counter-terrorism efforts and receives billions in aid from the U.S. In his 2012 budget, President Obama requested nearly $3 billion in foreign assistance for Pakistan, including $1.58 billion in funds for security-related programs.
Yet White House counterterrorism adviser John Brennan said yesterday that "it's inconceivable that bin Laden did not have a support system in [Pakistan] that allowed him to remain there for an extended period of time."
Bin Laden was killed in a three-story mansion complex in Abbottabad, a city about 40 miles north of Islamabad that's home to Pakistan's military academy.
Brennan said the administration is "closely" talking to the Pakistanis right now about the "support" bin Laden received, but Congress has its own questions.
"It's very hard for me to understand how Pakistani, particularly the ISI [Pakistan's main intelligence agency], would not have known that something was going on in that compound," Sen. Dianne Feinstein (D-Calif.), chairman Senate Intelligence Committee, said Monday. "I have had a growing concern that the Pakistani government, the Pakistani military and the Pakistani intelligence community is really walking both sides of the street, and the question comes what to do about it."
Pakistan's choice to remain allied with the U.S. would be a "much more positive choice for them long term," Feinstein said, but she added, "I don't think they've made that decision."
Feinstein also said U.S. financial support for Pakistan should be reviewed.
"Our government is in fiscal distress; to make contributions to a country that isn't going to be fully supportive is a problem for many," she said. "I want to think this out, talking to other members."
Rep. Steny Hoyer (D-Md.), the No. 2 Democrat in the House, also Congress should consider reducing U.S. aid to that country if concerns aren't allayed, the Associated Press reports.
"I don't know whether it would be effective or counterproductive, we'll have to look at that," he told reporters, adding, "It needs to be looked into."
Sen. Carl Levin (D-Mich.), chairman Senate Armed Services Committee, said on a conference call with reporters Monday that there are "a whole lot of unanswered questions here."
"I have some real discomfort about these facts here that seem to be so striking that it be almost impossible to conceive that the military .....and their intelligence did not know about this, the presence of this unusual compound," he said.
Sen. Susan Collins (Maine), the top Republican on the Senate Homeland Security Committee, said it was "very troubling" to her that Pakistan appears to be "playing a double game" with the U.S.
"We clearly need to keep the pressure on Pakistan, and one way to do that is to put strings attached to the tremendous amount of military aid we give the country," she said. "I do understand the Pakistan government is under tremendous pressure internally, but the fact is it is in Pakistan's own interest to work with us to defeat the terrorist threat."
Sen. Joe Lieberman (I-Conn.), chairman of the Homeland Security Committee, added that there will be "real pressure" on Pakistan "to basically prove to us that they didn't know that bin Laden was there."
Several leaders -- particularly from the Obama administration -- stressed the complex nature of the United States' relationship with Pakistan.
Brennan yesterday said it was understandable that congressional leaders were calling into question U.S. aid to Pakistan. But he called the U.S.-Pakistan alliance "critically important to breaking the back of al Qaeda and eventually prevailing over al Qaeda, as well as associated terrorist groups."
Both President Obama and Secretary of State Hillary Clinton in their public remarks this week cited counterterrorism assistance from Pakistan as a key part in the United States' fight against al Qaeda.
Pakistan's role in U.S. counterterrorism efforts will come into focus in the House today, where a Homeland Security subpanel is holding a hearing on the threat to the U.S. emanating from Pakistan.
House Intelligence Chairman Michael Rogers (R-Mich.) acknowledged yesterday the complexity of the U.S. -Pakistan allianced.
"Liaison partnerships are always -- they're never all-in propositions," he said. "You have to take the service as you find it in the country of which you find it. And they -- the ISI and Pakistan, the government of Pakistan - have been helpful to the United States when it comes to counter-terrorism actions and investigations."
Sen. Lindsey Graham (R-S.C.) said he understands the "frustration" of those who want to cut off aid to Pakistan, the AP reports.
"But at the end of the day, if you want to create a failed state in Pakistan, one of the best things to do is sever relationships," he said. "It is not in our national security interest to let this one event destroy what is a difficult partnership but a partnership nonetheless."
"Some in the U.S. press have suggested that Pakistan lacked vitality in its pursuit of terrorism, or worse yet that we were disingenuous and actually protected the terrorists we claimed to be pursuing. Such baseless speculation may make exciting cable news, but it doesn't reflect fact," Zardari wrote.
However, CBS News chief foreign affairs correspondent Lara Logantoday that the Pakistani government is not doing everything it could in its partnership with the U.S.
"And more importantly, they're not going to do everything that counts," she said.
Some groups, including networks linked to the Taliban -- some of which were created explicitly by the nation's security agencies -- which have broader anti-Western and anti-U.S. aspirations are given too much freedom, Logan said.
"Clearly, Americans are not getting a good return on their investment" in aid to Pakistan, Logan said, "and the Pakistanis have some explaining to do."
Watch Logan talk about U.S. relations with Pakistan on CBS' "The Early Show":