The Argentine military junta had ideas plans drafted for potential wars with the United Kingdom and Chile. Perhaps they'd have enacted one of them if they saw a need to bolster their regime (assuming no Democratic transition).
Thatcher left the Falklands pretty vulnerable. Perhaps the OTL already pretty-smashing alliance victory of over 50% would be even greater TTL with the negative impact of a lost war?
50% between two parties mind. The FPTP Voting System tends not to allow smaller parties to break through until a critical threshold is attained. Selective Seat Contesting and backing each other tipping the balance here and letting them govern as a Coalition.
Mondale's administration was broadly defined by three things: Foreign Policy Centrism, the failed attempt at the Equal Rights Amendment, and deficit hawkery.
Reagan probably makes deficits and tax cuts the defining political tendency instead of tight money and small deficits, the hallmark of the Carter-Mondale years. Reagan would be more hawkish, boosting defense budgets (and hurting deficits) and pushing for a nuclear buildup - in contrast to Mondale's nuclear freeze (which was good for the budget, although the Soviets got a bit pushier about things...). Mondale failed to get the ERA through, suffered a political loss, and proceeded to face the Conservative Revolution of 86' and be ousted by Conservative Icon Donald Rumsfeld in 1988.
If Carter loses, expect more hawkishness, bigger deficits, bigger tax cuts, and maybe a looser monetary policy.
OOC: The 1980's have already been referred to here as being a Democrat Decade, so Republicans seizing power starting in '86 doesn't gel well with that. If it started in '88 - '90, that would be more plausible.
IC: Thinking about it, when the Republican Return (which IIRC is how the 1990's are known as), began as the economy started going South again. The more Deficit-Spending-Willing Republican Policies able to be enacted in just as the recession began.
Small wonder they got accredited with reviving US Economic Fortunes at that critical moment, allowing them to Control all Three Houses starting in 1992. The USSR falling apart at about the same time is also a contributory factor here IMHO. *
Speaking of, I suppose in Reagan won in 1980, a major increase in military expenditure (as others have stated) could well have seen the USSR collapse sooner than it did IOTL. Say, about '88-'89?
* - OOC: I'm assuming here that with a less aggressive military spend in the US, the USSR wouldn't plow as much into theirs to maintain parity, so could limp on for just a very little bit longer.