GOP presidential candidate Newt Gingrich has a history of promiting clients of a think tank he founded in 2003, but without disclosing that they were clients, USA Today reported on Thursday.

In columns and speeches on ways to reform the health care system, the presidential candidate and former House speaker has celebrated clients of the Center for Health Transformation without noting the connection between the company, the think tank, and himself, USA Today reported.

Gingrich has been under fire for failing to fully disclose $1.6 million to $1.8 million in consulting fees he received from mortgage giant Freddie Mac after he left Congress. He has denied that any of the consulting involved lobbying.

Here are a few examples of Gingrich's disclosure problem, as compiled by USA Today: