I keep circling back to an issue that just won’t disappear.

Those tax returns that Donald J. Trump insists on keeping secret might answer a lot of questions about the president of the United States and his reluctance to say anything negative about Russia and its president/strongman/killer Vladimir Putin.

Trump won’t release them. He is dismissing a four-decade-old custom for presidential candidates and for presidents. They’ve all released them for public review. Except the current president.

I keep asking: How come? Trump keeps yapping about an “audit.” Two points here: The Internal Revenue Service — which doesn’t comment on specific audits — says an audit does not prevent someone from releasing those returns to the public; furthermore, Trump never has even proved that the IRS is auditing him.

He demanded repeatedly that Barack Obama produce a birth certificate to prove his constitutional eligibility to serve as president. How about Trump provide a letter from the IRS that declares that he’s being audited?

Amid all this is the swirl of Russia and whether the president has business dealings with Russian oligarchs and government officials. The president says he has none. He expects us to believe him. Sure thing, Mr. President. He also expected us to believe that Barack Obama wiretapped his campaign offices, that millions of illegal immigrants voted for Hillary Clinton and that thousands of Muslims cheered the collapse of the World Trade Center on 9/11.

Tax returns would reveal whether the president has any business dealings in Russia. If he has been telling us the truth about that matter, then the returns would validate his assertion. Wouldn’t they? If he’s not being truthful, well, the returns would reveal that, too. Am I correct on that?

I am left only to conclude that the tax returns the president refuses to release to the public contain something he doesn’t want us to see. Do they involve Russia, Mr. President? Do they reveal why you won’t speak ill of your pal Vlad Putin?