U.S. presidential election, 1984

[they don't love you like i love you]

the deficit spending of the '80s ... basically led to the demise of the USSR,

Balderdash.  That is one of those oft repeated bits of propaganda that people have come to accept as true, with little evidence.

Do you have any evidence otherwise?

Of course not.  It is the responsibility of the propagandists making the claim to make a case for it.  I'm not going to attempt to prove a negative. 

The cause of the demise of the Soviet Union can be summed in two words: Mikhail Gorbachev.

[Jake]

Actually, it can be summed up in one: Economy

Gorbachev was forced to make the decisions he made because the Soviets were seeing the reality that their command economy was collapsing. Without Gorby's actions, they may have held on longer or shorter, but their fall was inevitable sometime before the turn of the century, probably sooner. Now, this fall probably wouldn't have been as peaceful as OTL, and that's Reagan's important legacy. Carter probably could've overseen the fall of the USSR, nukes may have flown though.

[Frodo]

Reagan