Maddow said that when Johnston alerted her show on Monday to his interesting find, and offered to let her break the news, “we gave it a qualified ‘yes,’ provided we could verify it according to our own standards and were comfortable that we had met the NBC standards.”

Maddow said she and her research staff worked overnight Monday and all day Tuesday to assure themselves that the tax return was genuine, consulting with outside experts before contacting the White House.

“We knew that was the bell we had to ring before we could go with it,” Maddow said. “There were a number of scenarios. They might have no-commented or said outright it was fake.”

If the White House had done either, “We were ready with a whole different show that was not about tax returns,” Maddow said. “We had a whole different A-block ready to go, we’d booked different guests. But at the very last minute we were comfortable that we had the verifications that we needed.”