Only two weeks after President Bush asked Donald Rumsfeld (search) to stay on for his second term, the drumbeat has grown louder for the secretary of defense to resign.

Calls for Rumsfeld's head increased after a national guardsman asked him during a trip to Kuwait why some soldiers in Iraq were still traveling in unarmored vehicles and sometimes had to scrounge for scrap metal and glass to protect their trucks and Humvees (search).

Rumsfeld's controversial response was: "You go to war with the Army you have, not the Army you might want or wish to have."

The defense secretary explained that shortages of armor were "a matter of physics, not a matter of money," suggesting that production lines were operating at capacity.

Both Rumsfeld and Bush have said more vehicle armor would be shipped to Iraq; the Army has promised more than $4 billion to beef up equipment in both Iraq and Afghanistan.

Seventy-eight percent of Humvees in Iraq, Afghanistan and Kuwait have protective armor. But only 10 percent of medium-weight transport trucks, and only 15 percent of heavy trucks, do.

Six Ohio-based reservists have been court-martialed for commandeering Army vehicles abandoned in Kuwait by other units to carry out their own unit's mission into Iraq.

Rumsfeld's response to the questioning in Kuwait has brought on a surge of criticism, with calls for his head coming from both sides of the aisle.

Congressional Black Caucus Chairman Elijah E. Cummings, D-Md., on Friday cited the allegations of Iraqi prisoner abuse at Abu Ghraib (search) prison and the vehicle armor issue as two reasons Rumsfeld should exit the Pentagon.

"I trust that our bipartisan voices will now be heard by President Bush and the Republican leadership, and Mr. Rumsfeld will make the right decision to leave his post. This is too critical a time in American history for further colossal mistakes to be made that put the future of our country at risk," Cummings said in a statement.

But the White House defended Rumsfeld once again on Friday.

"Secretary Rumsfeld is doing a great job leading our efforts at DoD to win the War on Terror and help bring about free and peaceful Iraq," said spokesman Scott McClellan.

Sen. John McCain (search), R-Ariz., was the first to criticize Rumsfeld, although he stopped just short of calling for the secretary's resignation, saying Bush should "have the team that he wants around him."

Citing the Pentagon's failure to send more troops to Iraq, the former Vietnam prisoner of war said 80,000 more soldiers and 20,000 to 30,000 more Marines were needed to secure Iraq, especially as the country gears up for the Jan. 30 elections.

"I have strenuously argued for larger troop numbers in Iraq, including the right kind of troops — linguists, special forces, civil affairs, etc.," McCain told The Associated Press in an interview. "There are very strong differences of opinion between myself and Secretary Rumsfeld on that issue."

Former Senate Majority Leader Trent Lott, R-Miss., said this week that Rumsfeld should leave office sometime in 2005.

"I'm not a fan of Secretary Rumsfeld," Lott reportedly told the Biloxi Chamber of Commerce Wednesday, adding that more U.S. troops were needed and a more solid plan must be put together for leaving Iraq after the elections. "I don't think he listens enough to his uniformed officers ... I'm not calling for his resignation, but I think we do need a change at some point."

Sen. Mark Dayton (search), D-Minn., sent a letter on Wednesday to Bush, urging the president to immediately request an investigation into why the proper armor and equipment were not ordered and distributed to U.S. troops stationed overseas. Dayton told FOX News on Friday that no matter where the buck stops, someone must be held accountable.

Dayton, who sits on the Senate Armed Services Committee, noted in his letter that as recently as Nov. 10, during a briefing before the panel, lawmakers "repeatedly asked the presenting military officers and Pentagon officials whether everything possible was being done to retrofit unarmored vehicles already in Iraq and Afghanistan, and to produce new armored vehicles for those theaters."

"Again and again," Dayton wrote, "we were assured that everything possible was underway, and that Congress had provided all of the funding necessary to fill those terrible deficiencies as rapidly as possible."

Rep. Martin Meehan (search), D-Mass., told FOX News that he was "very disappointed" at Rumsfeld's response to the armored-vehicle issue.

The House Armed Services Committee, which Meehan sits on, has repeatedly asked the Pentagon if it has all the money it needs to protect U.S. troops overseas, and the agency has repeatedly been too slow to respond, he said.

"Frankly, I think the buck stops with the secretary of defense," Meehan said.

Sen. John Corzine (search ), D-N.J., actually has called on Rumsfeld to resign.

"I believe this isn't the issue only of Humvees," Corzine told "FOX News Sunday." "The miscalculation and interpretation of the intelligence before the war — there was a failure to secure all the weapons dumps ... there's been a problem with our administration of the prisons. No one has been held accountable. There's no exit plan."

"I think, at some point, someone needs to be held accountable for all the series of mistakes and miscalculations we've had," he added.

Weekly Standard editor and FOX News contributor William Kristol (search) said Rumsfeld had been so focused on transforming the military into a lighter, quicker force, that issues such as troops levels in Iraq had not received enough attention.

"Look, Rumsfeld is an impressive guy ... but I think a lot of us think that after Jan. 30, after the Iraq elections, the president would be better served by a new secretary of defense," Kristol said on Friday, adding that it's no secret Bush has been "frustrated" with Rumsfeld.

But not everyone thinks Rumsfeld should quit.

Sen. Lindsey Graham (search), R-S.C., told FOX News that the defense secretary had provided invaluable leadership amid a tumultuous situation in Iraq.

"War is a messy thing," Graham said. "The insurgents are ruthless people. We're trying to adapt. We have made mistakes.

"We need to adjust. I don't wish to play politics with this. Let's give the people what they need. Let's press on and learn from our past mistakes."

Sen. Mitch McConnell, R-Ky., said the kind of progress being made in Afghanistan and Iraq isn't easy and Rumsfeld is to be thanked for the successes achieved.

"And while Secretary Rumsfeld has my full support, more importantly he has the president's," McConnell said.

California Rep. Duncan Hunter (search), the Republican chairman of the House Armed Services Committee, told FOX News that Rumsfeld had done an outstanding job at the helm of the Defense Department, despite the numerous challenges facing him and the military in the past few years.

"Donald Rumsfeld has done a good job. He's probably got the most difficult challenge of any secretary in years," Hunter said, citing Rumsfeld's ongoing efforts to transform the nation's military, successfully conduct wars in Iraq and Afghanistan and deal with the ongoing nuclear threats posed by countries such as North Korea and Iran.

"This secretary has his hands full," Hunter added. "He's one of the few guys who can handle lots of problems at the same time, and I think he's walked us through a very difficult situation in Afghanistan and Iraq ... I think he's done a good job and should stay on."

Rumsfeld has recently said he looks forward to pursuing unfinished business, including the war in Iraq. He did not say he would stay for Bush's full second term, but he left the impression that he expects to.

"The president asked me if I would be willing to stay on, and I told him I would be delighted to do that," Rumsfeld said on Dec. 6.