Washington becomes latest state to push plan to force President Trump to release tax returns. Here's their plan.

The Washington state Senate last week passed a bill that would prevent President Donald Trump's name from appearing on the state's 2020 presidential election ballot should he not release his personal tax returns, a customary tradition of presidential candidates.

What are the details?

The proposal would mandate that presidential candidates release five years worth of personal tax returns before appearing on the ballot in the primary or general election, The Associated Press reported.

The bill advanced to the state House of Representatives last Tuesday after the state Senate approved it by a 28-21 vote.

State Sen. Patty Kuderer (D), the bill's primary sponsor, claimed that candidates' tax returns have become "part of the vetting process" for voters.

"Although releasing tax returns has been the norm for about the last 40 years in presidential elections, unfortunately we've seen that norm broken," she said, according to AP.

Meanwhile, opponents of the provision believe the bill would add qualifications for the office of president and vice president outside of the Constitution. Others voiced concerns about the message, and potential implications, such a law sends.

"We're on really risky ground when we're trying to place conditions on a federal election," state Sen. Hans Zeiger (R) said.

"I just don't understand why in the world you would promote something that would connote that there's something suspicious about the activities of our elected officials," state Sen. Maureen Walsh (R) explained.

Is the law constitutional?

The Constitution in Article 2, Section 1 clearly outlines the legal qualifications for president:

• Must be a natural-born citizen
• Must be at least 35 years old
• Must permanently live in the U.S. for at least 14 years prior to election

The Constitution does not list a presidential qualification for releasing financial information, let alone personal income tax returns, which did not exist until the 20th century.

However, legal experts told the Associated Press some ambiguity exists because the Constitution also enumerates power for each state to determine rules guiding presidential elections.

In fact, Washington state Attorney General Bob Ferguson and solicitor general Noah Purcell told state lawmakers in a letter last week that the law would be "likely Constitutional," although they warned it would face earnest challenge in court.

What's the background?

Trump's tax returns have been a major point of contention thorough his short political career. His detractors believe they might contain evidence of impropriety or criminal activity.

During the 2016 presidential election, Trump said he would not release his tax returns because he was under audit by the Internal Revenue Service.

More than two dozen states are considering similar legislation in light of Trump's refusal to make public his personal returns, the AP reported. New Jersey lawmakers approved a similar measure in 2017, but Republican Gov. Chris Christie vetoed it, calling a political stunt.