An FBI investigation, investigation by Congressional committee, DOJ investigation into the Clinton Foundation, and now the IRS — yet, Hillary’s still polling above 50%.

A Dallas-based IRS office is digging into the Clinton Foundation and why the entity remains tax exempt.

While the foundation’s bookkeeping appears rather solid and above reproach, as Joe Pappalardo from the Dallas Observer reports, whether Hillary used the foundation to buy influence and favors as Secretary of State is where the story gets a bit sticky.

The piece is lengthy, but well worth the read. The CliffsNotes are beneath:

Why the Dallas Office?

As with anything tax related, the status of the foundation may be determined using rules few understand. And that makes understanding the work at 1100 Commerce St. in Dallas that much more important.

In Washington, D.C., many things start with words printed on congressional letterhead. Earlier this year, 64 GOP members of Congress asked the IRS to investigate why the foundation can keep its nonprofit status. The letter includes “media reports” claiming pay-to-play relationships between former President Bill Clinton, who received large speaking fees, and decisions made by Hillary Clinton to approve choices that benefited foundation donors. The sources of these reports range from The New York Times to hit-piece investigative books.

In July, the IRS sent letters back to the Congress informing members the review had begun. The letter also noted that the Tax Exempt and Government Entities Division (TE/GE) office in Dallas would be conducting the review.

IRS spokespeople in Dallas and Washington won’t say why the review is being conducted in Dallas. Spokespeople claim even this information would violate rules — Code 6103, staff make sure to cite — that stop them from discussing ongoing examinations. IRS officials declined to provide details about the Dallas office, including its size, or comment on the TE/GE work in general.

Why are they looking?

The strategy is focused on big money charities: “Our examinations will cover all gross wage categories but with an emphasis on entities with gross wages of $10 million or more; approximately 75 percent of examination closures will be of these returns.”

In 2014, the Clinton Foundation tallied its salaries at more than $26 million, according to IRS filings. So that puts the Clinton Foundation square in the middle of the Work Plan’s enforcement strategy.

Why is the Clinton Foundation tax exempt?

The case against the Clinton Foundation is multifaceted. One common attack is that the foundation has overextended its original mandate. “The Foundation’s original application to the IRS in 1997 advised that it was formed to construct a library, maintain a historical site with records, and engage in study and research,” said Tennessee Republican Rep. Marsha Blackburn in an email to the Observer. “It did not indicate an intent to conduct activities outside of the United States, which was on one of the codes included in the IRS ‘Application for Recognition for Exemption’ in effect at the time. This would appear to prohibit much of the overseas work the Foundation has performed.”

Is there a case against the Clinton Foundation?

Using a nonprofit group for personal enrichment — called inurement — is one sure-fire way to gain IRS scrutiny.

In the case of the Clinton Foundation, it’s not exactly a matter of stealing from the cookie jar. The bookkeeping — with documents available for public as well as IRS scrutiny — appears sound since the IRS has not raised any red flags. The foundation spends a solid 88 percent of its money on actual programs, according to the group Charity Tracker. That’s pretty good ratio of overhead to actual charity work.

But the Clinton Foundation problem is more nebulous. The central question is not exactly one the IRS can easily track: Did the founding members trade influence for donations, especially while Hillary Clinton was secretary of State?

Clinton and her staff have consistently denied any conflicts of interest or improper enrichment and cite reporting holes in the media stories and books claiming pay-to-play relationships. But since July, more information has been revealed, via hacked email correspondences of Clinton adviser John Podesta released by Wikileaks.

The emails reveal that Chelsea Clinton ordered an audit of the foundation and “some interviewees reported conflicts of those raising funds or donors, some of whom may have an expectation of quid pro quo benefits in return for gifts.”

Given this language, citing “gifts” and “quid pro quo benefits” in emails is a pretty bad move for anyone involved in a nonprofit group. Another bad move: When senior Clinton advisers like Doug Bland call the intersection of the foundation fundraising and the former president’s personal activities “Bill Clinton Inc.”

It’s hard to imagine a chink in the Clinton Empire armor. They’ve escaped unscathed from investigation after investigation, but not even Al Capone could escape the long arm of the IRS.

Follow Kemberlee on Twitter @kemberleekaye