It was a shame but not all that surprising when the awaited encounter between President Obama and his Iranian counterpart, Hassan Rohani, didn’t happen Tuesday at the U.N.

Obama offered to shake Rohani’s hand, but the invitation was declined. The last time the two countries’ leaders met was 36 years ago, during the reign of Shah Mohammed Reza Pahlavi. He’d been installed in a U.S.-backed coup, only to be overthrown in 1979 by Islamic revolutionaries who held 52 Americans hostage for 444 days.

In other words, there’s a lot of history here. But over the years, what each country wants from the other hasn’t much changed. The Iranians want to be treated with respect, and the Americans want Iran to behave respectably, especially when it comes to Iran’s nuclear program.

The Iranians say they’ve no intention of building nuclear arms and have a right to nuclear technology, including uranium enrichment. Fine, as long as Iran meets Nuclear Non-Proliferation Treaty obligations and submits its nuclear installations to International Atomic Energy Agency inpection.

The U.S. should relieve Iranian anxieties by stating that it can live with a limited Iranian enrichment capacity. That would go a step beyond Obama’s statement to the U.N. that Iran has the right to civilian nuclear power.

At the same time, if the Iranians want to be believed when they say their program is innocuous, they’d do well to stop insisting, as Rohani has in recent days, including at the U.N., that Iran has never sought nuclear arms. The U.S. and its allies collected strong intelligence showing Iran had such a program until it halted the work in 2003.

Some members of Congress support increasingly severe sanctions on Iran, but Congress will have to allow the diplomats to test whether the punishments already in place have created an opening for meaningful talks. A settlement could offer the lifting of sanctions in stages as Iran meets its IAEA obligations. That would be a good result — but to get there, each side must first convince the other that it’s serious.