On May 24, U.S. Senator Ron Wyden (D-Oregon) introduced the “Presidential Tax Transparency Act”. It requires the U.S. Treasury to release copies of the tax returns of presidential candidates to the Federal Election Commission. Then, the FEC would release them to the public. See this story.
The bill would only apply to the presidential nominees of a party that polled at least 25% of the popular vote in the last presidential election.