WASHINGTON (Reuters) - Mass protests against Hosni Mubarak, the president of Egypt for the last three decades, are prompting questions about how the United States should respond to an authoritarian leader who has been its long-time ally.
Secretary of State Hillary Clinton on Sunday urged an orderly transition to democracy in Egypt but stopped short of calling on Mubarak to step down as Washington sought to avoid a power vacuum.
Below are key questions about the U.S.-Egyptian relationship, drawn chiefly from reports released this week by Jeremy Sharp of the Congressional Research Service, the non-partisan research arm of Congress, and by Jon Alterman of the Center for Strategic and International Studies think tank in Washington.
Egypt's decision in March 1979 to become the first Arab state to sign a peace treaty with Israel cemented its relationship with the United States and has resulted in its receiving an annual average of $2 billion in U.S. aid in the years since.
The treaty has been vital to Israel, a close U.S. ally, allowing it to worry less about its western flank and setting a precedent it hoped might lead a wider Arab peace. However, only Jordan has followed suit in signing a peace deal with Israel.
Egypt has been particularly helpful to the United States in promoting Arab-Israeli peace, counterterrorism and helping the movement of U.S. troops and equipment around the Middle East.
Egypt's Suez Canal links the Mediterranean with the Gulf of Suez and is a vital shipping route between Europe and Asia.
Successive U.S. governments have viewed Egypt as a bulwark of stability and as a moderating influence on the region.
With a population of some 80 million, the largest in the Arab world, Egypt has a regional weight bolstered by its citizens working in many Arab nations and by its films and TV shows, seen throughout the Middle East.
Former President George W. Bush antagonized the Egyptian authorities by publicly pushing hard -- but with no visible success -- for greater political reform in the country.
In an unusually harsh move toward an ally, his Secretary of State Condoleezza Rice postponed plans for a visit to Egypt in 2005, when the United States was particularly concerned about the jailing of Egyptian opposition politician Ayman Nour.
The Bush administration subsequently moderated its stance toward Egypt, recognizing that the tough public line had not brought the political change it had sought and seeking Egyptian backing as it tried to revive Israeli-Palestinian peace talks.
On coming into office, the Obama administration appeared to try to heal some of the wounds from the Bush years.
Obama selected Cairo as the venue for his June 2009 outreach to the Arab world, giving a speech to build bridges despite the widespread Arab outrage at the March 2003 U.S. invasion of Iraq and the country's subsequent bloodletting.
In careful, general terms, Obama said he had an "unyielding belief" that all people want to speak their minds, to have a say in how they are governed, to enjoy equal treatment under the law and to have governments that do not steal from them.
"Governments that protect these rights are ultimately more stable, successful and secure," he said.
Obama invited Mubarak to the White House last year along with the leaders of Israel, Jordan and the Palestinian Authority as he relaunched Israeli-Palestinian peace talks.
Over the last 30 years, Egypt has been the second largest recipient of U.S. foreign aid after Israel.
In the fiscal year to September 30, 2010, it received $1.5 billion, including $1.3 billion in military aid and $250 million in economic aid. That year Egypt was the fifth-largest recipient of U.S. aid after Afghanistan, Israel, Pakistan, and Haiti.
The bulk of the military assistance goes to pay for Egypt's purchases of military hardware, upgrades to existing equipment and maintenance and support contracts.
Among the big ticket defense items that Egypt has bought from the United States are Lockheed Martin Corp F-16 fighters, M1A1 tanks, for which General Dynamics Corp is the prime contractor, and Boeing Co's CHINOOK transport helicopters.
The $250 million in economic assistance is divided among several sectors, including health, education, economic development and democracy promotion.
While the Egyptian government objects to aid to promote democracy, it has grudgingly allowed some such programs.
(Additional reporting by Jim Wolf; Editing by Vicki Allen and Eric Beech)
Sources: "Egypt: Background and U.S. Relations," by Jeremy M. Sharp, specialist in Middle Eastern Affairs at the U.S. Congressional Research Service; "Critical Questions: Events in Egypt" by Jon Alterman, director of the Middle East program at the Center for Strategic and International Studies