WASHINGTON  A few hours after getting off a plane from America’s war zones, Joseph R. Biden Jr. slipped into a chair, shook off his jet lag and reflected on what he had seen. The situation in Iraq, he said, was much improved. In Pakistan, he said he saw encouraging signs.

Then he came to Afghanistan and shook his head.

“It has deteriorated significantly,” he said. “It’s going to be a very heavy lift.”

That was six days before Mr. Biden was sworn in as vice president in January, and just after he had met with President-elect Barack Obama, who had sent him on the fact-finding mission to figure out just what the new administration was inheriting. Mr. Biden’s assessment was even grimmer during his private meeting with Mr. Obama, according to officials.

From the moment they took office, Mr. Biden has been Mr. Obama’s in-house pessimist on Afghanistan, the strongest voice against further escalation of American forces there and the leading doubter of the president’s strategy. It was a role that may have been lonely at first, but has attracted more company inside the White House as Mr. Obama rethinks the strategy he unveiled just seven months ago.