Mueller Should Subpoena Trump to Trigger Constitutional Showdown: Republicans for the Rule of Law Adviser

A USA Today opinion piece by Chris Truax is suggesting special counsel Robert Mueller should subpoena President Donald Trump rather than negotiating for a voluntary interview.
The op-ed argues that acquiescing to Trump out of fear the president will trigger a constitutional crisis is harming our system of checks and balances.
"Giving Trump special treatment out of fear he will provoke a constitutional crisis by ignoring a grand jury subpoena only weakens those institutions for the next confrontation," Truax writes.
Traux argues that the president has no legal claim to avoid a subpoena.
He explains:
The president is merely a citizen entrusted with high office. While the courts must pay due deference to the president’s constitutional responsibilities, he is no more entitled to violate the laws or ignore a court order than is any other citizen. Like any other citizen, he has a duty to provide evidence in response to a grand jury subpoena.
Traux concludes that the best outcome from a confrontation between Trump and Mueller would be a "firmly-established principle that no one, including the president — especially the president — is above the law."