The Clinton Foundation tackles some of the world's biggest problems, from hunger to climate change. But it's also creating problems for Hillary Clinton.

Critics, including Bernie Sanders and Donald Trump, have used the Clinton Foundation as a political weapon. Their claim is that the nonprofit's acceptance of donations from other countries while Clinton was Secretary of State created a conflict of interest and could do so again if she's elected president.

Richard Davis, a Clinton supporter and former assistant Watergate prosecutor, said the Clinton Foundation should eliminate foreign financing altogether.

"I think it would be important for her to make clear right now that if she's president, the Foundation will not take money from any foreign interests, and will not take money from anybody, whether it's an individual or a company, that does business with the United States government, or plans to do business with the United States government," Davis said in a recent interview with CNNMoney.

One of Clinton's harshest critics, author Peter Schweizer, is pushing for a federal government investigation of the Foundation, though he concedes he has no evidence of wrongdoing.

The complex structure of the organization -- along with its vast network of donors -- makes it difficult to evaluate.

The Clinton Foundation lists 300,000 contributors and 11 different initiatives, from lowering the cost of life saving medicines to reducing greenhouse gas emissions. Foreign governments and corporations help fund the foundation's initiatives.

But the Clinton Foundation's extensive humanitarian work won't shield it from Trump's attacks on the campaign trail.

Last month, Trump called Clinton's role with the Foundation "a disgusting situation. ... The whole thing is a scam."

And some self-inflicted wounds by the Clinton Foundation have undermined its own assertions of transparency.

In 2008, the Foundation signed an ethics agreement with the Obama administration before Hillary became Secretary of State. The document outlined how the Clinton Foundation would address potential conflicts of interest.

Under that agreement, the Foundation needed to disclose its funding sources to the State Department. On at least one occasion, however, it failed to do so, omitting a report on a $500,000 donation from Algeria in 2010 for Haitian earthquake relief.

In addition, in response to a media inquiry, the Foundation refiled tax forms for 2010, 2011, 2012 and 2013 to break out government grants from other donations.

Last year, the Foundation confirmed that it failed to report as much as $26.4 million in speaking fees the Clintons received from foreign governments and corporations.

The Clinton Foundation says it has properly policed itself, finding and fixing the errors with regard to the Algerian donation and the undisclosed speaking fees. It also has a top rating from two charity watchdog groups.

After Hillary Clinton announced her bid for the White House, the Clinton Foundation took additional measures to allay concerns about transparency. It reduced the number of nations from which it would accept donations to six countries: Australia, Canada, Germany, the Netherlands, Norway and the United Kingdom. But Davis, who is a Clinton supporter, says that's not enough.

"If you want to be president of the United States, there are just certain things your family cannot do."