On Thursday, the New York State attorney general sued the Donald J. Trump Foundation, charging it with “improper and extensive political activity, repeated and willful self-dealing transactions, and failure to follow basic fiduciary obligations or to implement even elementary corporate formalities required by law.”

The lawsuit follows years of scrutiny of President Trump’s charitable activities and adds to the president’s extensive legal challenges, amid a continuing investigation by special counsel Robert S. Mueller III.

What is the Trump Foundation?

Mr. Trump established the Donald J. Trump Foundation in 1987, when he was a New York City real estate mogul, with the stated mission of collecting and maintaining money “exclusively for charitable, religious, scientific, literary or educational purposes,” either directly or by donating to other organizations. It is a private, nonprofit corporation. In its most recent I.R.S. filing, reporting as of Dec. 31, 2016, it had approximately $1 million in assets.