Presumptive GOP presidential nominee Mitt Romney said, "I am pleased that President Obama has returned to Afghanistan."
"Our troops and the American people deserve to hear from our president about what is at stake in this war," he said. "Success in Afghanistan is vital to our nation's security."
More than 130,000 troops from 50 countries serve in Afghanistan. The United States is the largest contributor, providing some 90,000 troops, followed by the United Kingdom (9,500), Germany (4,800) and France (3,600).
But war that began with widespread approval in 2001 is now increasingly unpopular in Europe and the United States. The latest CNN/ORC International poll in late March show 55% of respondents would like to see the U.S. remove all its forces before 2014.
More than 2,700 troops from the United States and its partners have died in the conflict. The majority of them American.
Last week, Afghan National Security Adviser Rangin Daftar Spanta and U.S. Ambassador Ryan Crocker initialed the text that outlined the kind of relationship the two countries want in the decade following the NATO withdrawal.
The deal had been long expected after Washington and Kabul found compromises over the thorny issues of "night raids" by U.S. forces on Afghan homes and the transfer of U.S. detainees to Afghan custody.
It seeks to create an enduring partnership that prevents the Taliban from waiting out a U.S. withdrawal to try to regain power, the senior administration officials have said.