Washington ? President Bush’s performance as commander-in-chief was supposed to be his strong suit in the November election, but questions about his leadership suddenly have forced him on the defensive.

With the week only half over, Bush had reversed course on the need for an investigation into prewar intelligence in Iraq, reluctantly agreed to extend an investigation into the Sept. 11 terrorist attacks and fended off questions about his military service.

In a clear sign of potential political damage, a new Gallup poll shows that voters trust Sen. John Kerry of Massachusetts — the front-runner for the Democratic presidential nomination — more than Bush to decide when U.S. troops should go to war. And, for the first time since the U.S.-led invasion of Iraq, fewer than half of Americans — 49 percent — say the war was worth it.

“If that goes below 50 percent and stays there, it’s a real significant problem for the Bush administration,” said Frank Newport, Gallup’s editor in chief. “All the discussion about the rationale (for war) is beginning to have some effect on Americans.”

The poll, conducted for CNN and USA Today from Jan. 30 to Feb. 1, also showed the president’s overall approval rating at a new low of 49 percent. Any approval rating below 50 percent is considered a clear warning sign for a candidate seeking re-election.

The poll, of 1,001 adults, was conducted nationwide Jan.30-Feb. 1, with an error margin of plus or minus 3 percentage points.

Bush has made his wartime leadership the centerpiece of his re-election campaign, but Kerry’s emergence as the Democratic front-runner and continuing problems in Iraq and Afghanistan could complicate the Republican game plan. Democrats already are trying to draw a contrast between Kerry’s status as a decorated Vietnam veteran and Bush’s gap-filled record as a member of the National Guard.

On Sunday, aides confirmed that Bush would appoint a special commission to investigate intelligence failures in Iraq and elsewhere. The president, who had resisted the idea of an outside investigation, decided to name his own panel in the face of pressure for an independent inquiry.

He also backtracked from his previous insistence on adhering to a strict May 27 deadline for a separate investigation into the Sept. 11 attacks. Faced with the possibility that Congress would force his hand, Bush agreed Wednesday to give that commission another 60 days to complete its work, pushing the deadline closer to the November election.

In the White House briefing room, spokesman Scott McClellan refused Wednesday to answer questions about the president’s military service during the Vietnam War. Democratic Party Chairman Terrence McAuliffe revived questions about Bush’s record over the weekend by suggesting that Bush went AWOL — absent without leave — in 1972.

Bush spent most of the year in Alabama working on a political campaign, but there’s no record that he ever reported to his assigned unit with the Alabama National Guard. White House aides say Bush fulfilled his obligation and note that he was honorably discharged.

“I think we went through this issue four years ago, and I went through this issue yesterday,” McClellan said when asked about it again Wednesday. “I will leave it where I left it yesterday.”

McClellan also refused to discuss Bush’s slip in the polls.