And what would this accomplish exactly?
What did breaking off relations with Iran accomplish?
Nothing? The regime is still there and it took decades for the U.S. to understand it's not going anyway so they might just as well try to mend tensions.
Russia, like Iran, has many legitimate grievances with the US. They don't justify Russia's behavior. But Bush 41 promised Gorbachev we would not expand NATO as we have done. If the Cold War ended less favorably to us, how would Americans feel if the still-intact USSR attempted to integrate Greece, Finland, Austria, and Italy into the Warsaw Pact?
Economic sanctions, breaking off relations, are acts of war. It is not in our interest to do this to Russia. Period.