Tapping big money donors for ambassadorial posts is a century-old White House practice, but one that is causing President Obama new headaches.

Three of Obama's ambassador nominees -- for Norway, Argentina and Hungary -- raised six-figure sums for his re-election campaign, helping him win a second term.

Modern presidents have regularly picked well-heeled campaign donors and political allies for plum foreign assignments. But the decades-long debate over the practice has flared up again after the three flubbed basic political facts about the countries they were picked to serve during their confirmation hearings.

Now career diplomats are pushing back.

The American Foreign Service Association (AFSA), the union group for career diplomats, is reviewing the Certificates of Demonstrated Competence for nominees that the State Department fills out and submits to the Senate Foreign Relations Committee before hearings. The group is weighing their qualifications and its next move.

Even obtaining those documents was a struggle for AFSA. The State Department allowed the union's Freedom of Information Act request for the certificates to languish for months, only complying after the group threatened to file a lawsuit and raise a stink during a press briefing at which reporters pushed the administration on the matter.

Others are pressing Obama to withdraw the nominations altogether.

After the FOIA dust-up, 15 former AFSA presidents wrote a letter to top senators on Capitol Hill, urging them not to confirm the nominees for Norway, Argentina and Hungary.

“The fact that they appear to have been chosen on the basis of their service in raising money for electoral campaigns, with minimal demonstrated qualifications for their posts, has subjected them to widespread public ridicule, not only in the U.S. but also abroad,” they wrote.

The 15 signatories to the letter feature many distinguished former career diplomats, including Thomas Boyatt, a former ambassador to Colombia and Burkina Faso, who was held captive for six days after Palestinian terrorists hijacked his flight in 1969.

Amid the crisis in Ukraine and two years after the attack on the U.S. Consulate in Benghazi, current and former Foreign Service officers say the administration needs to insure that qualified ambassador candidates are posted around the globe.

“We don't know where the next hot spot is going to pop up,” AFSA spokeswoman Kristen Fernekes told the Washington Examiner.

Presidents generally follow a “70-30” rule when making the nominations, choosing career Foreign Service officers for the majority of posts and leaving the rest for big donors and others who helped on the campaign.

AFSA keeps a close watch on the ratio and says political allies have accounted for 37 percent of the ambassadors so far during Obama's time in office but that number rises to 53 percent if only those nominated in his second term are counted.

But it's the cringe-worthy congressional testimony from the current crop of nominees that has the diplomatic corps up in arms.

In grilling Norway ambassador nominee George Tsunis earlier this year, Sen. John McCain, R-Ariz., pointed out that Tsunis had offered a generous assessment of the country's president even though it didn't have one. Norway is a constitutional monarchy, McCain chided.

Colleen Ball, the soap-opera producer who created “The Bold and the Beautiful” and was chosen by Obama to represent him in Hungary, stammered when identifying U.S. strategic interests in the central European country that shares a border with Ukraine.

And Noah Mamet, a longtime Democratic operative and Obama's choice for ambassador to Argentina, said he has traveled extensively in his life – but not to Argentina.

The White House, though, has defended the picks, with press secretary Jay Carney saying that Obama has “confidence” in all of his nominees.

Henri Barkey, a State Department official during the Clinton administration and an early supporter of Obama in 2008, said the president's appointments “suggest that he isn't being honest when he says that diplomacy is important to him.”

Barkey, now a professor of international relations at Lehigh University, told the Examiner that “all administrations appoint lousy bundlers,” but in this case Obama’s picks had not bothered to do their homework and don't deserve to be confirmed.

“Even though I am an Obama supporter, when you make mistakes you have to live with consequences and admit you erred. I think the president should withdraw them,” he said in an email.

If Obama were “to pull the plug on these nominees, he would also be establishing a standard,” Barkey said.