The top senator on the Armed Services Committee is urging President Obama to stop insisting that Afghan President Hamid Karzai sign a post-war agreement with the U.S. and instead let a “more reliable” successor close the deal.

Sen. Carl Levin, D-Mich, who chairs the panel with oversight of all military operations, penned a letter to Obama on Thursday expressing concern that U.S. insistence on having Karzai sign the bilateral security agreement by the end of the year is contributing to a mistaken belief that America needs the the agreement more than Afghanistan.

If Karzai chooses not to sign the pact, “the next Afghan president, whoever he is, is also likely to be more reliable than President Karzai, and there would be greater confidence in his sticking with an agreement he has signed,” Levin wrote.

Karzai, who U.S. officials already regarded as an untrustworthy partner, two weeks ago balked — at the last second — over signing a post-war security pact with the United States that would set troop and U.S. assistance levels after 2014.

The Afghan leader has repeatedly told the U.S. that he will not sign the agreement unless the White House agrees to a new set of last-minute demands, including expanded peace talks with the Taliban and the release of 17 Afghan detainees from Guantanamo Bay.

The text of the agreement was settled months ago after an arduous year-long negotiation and approved by a council of Afghan elders, known as the Loya Jirga.

The White House has pushed back, with National Security Adviser Susan Rice demanding that Karzai sign the agreement by December or face the reality of a complete U.S. withdrawal from Afghanistan -- including all U.S. troops as well as the billions the U.S. had planned to provide the country in financial aid.

The administration had hoped to leave a residual force of 8,000 in troops to train Afghan military forces and safeguard humanitarian operations after the war.

But Levin on Thursday said Afghanistan needs U.S. support more than it needs Karzai to cooperate. If neither Karzai nor his successor signs the agreement, Levin said the U.S. should pull all of its troops out of Afghanistan.

“NATO is already planning for all options, including a zero option,” he wrote. “We should be clear, however, that such planning is not intended as a threat but rather is the responsible actions of our civilian and military leaders.”