I may have misspoke….
Death and state funeral of Leonid Brezhnev
https://en.wikipedia.org/wiki/Death_and_state_funeral_of_Leonid_Brezhnev
Speaking at a Veterans Day ceremony, American President Ronald Reagan called Brezhnev “one of the world’s most important figures for nearly two decades” while expressing his hope for an improvement in Soviet–US relations.[76] Reagan then visited the Soviet embassy in Washington, D.C., on 13 November to sign a message in the embassy’s condolence book.[77] Reagan later described having “a strange feeling in that place”, noting how no one, except the ambassador, was smiling.[78] Ambassador Anatoly Dobrynin noticed Reagan appearing “guarded and very inhibited when entering the embassy ... wondering what kind of place it was”, but stated that Reagan seemed “more in his element by the end of his visit”.[79]
We had diplomatic relations with the Soviet Union. This is not analogous to the situation in Iran. The Iranians still occupy our Embassy compound in Tehran. They have turned it to a museum.
Hamas and Hezbollah are surrogates of Iran. Trump killed Soleimani. That should be the normal course of business.
In the Reagan era, the US and the USSR were adversaries but had normal diplomatic relations with each other for decades. The US and Iran do not have diplomatic relations. Neither do the US and Cuba.