I think Scoop would have trouble actually governing, but he could win merely because of the stigma to the GOP name in '76.
Scoop was an old school liberal, big on the New Deal and its expansion as well as the Cold War. The New Left despised people like him, and they wouldn't have gotten behind him, especially in Congress, where things like the Church hearings and attempts to prosecute Nixon officials were still the talk of the day. Congress in the mid to late 70s was a depressing atmosphere much like the rest of the country, and quite a few of them started openly advocating anti-American sentiment as part of their platforms.
Scoop would NOT give up the Panama Canal, nor would he cave on the hostage crisis. He might have cleaned up the army and gotten rid of drugs a lot sooner than OTL based on his fixation on defense issues. I think he would try to expand the war on poverty as well and pass more union friendly legislation. He might have been able to avert the Iranian revolution, might not have, but he would not have appeared as weak as Carter. I think he gets involved with the Contras earlier as well, and maybe helps Somoza stay in power.
But the atmosphere of the period was a truly awful one, and he'd have serious issues with the economy and keeping blue collar jobs from collapsing as OTL. I don't think he survives 1980, not unless he is somehow able to bring the Moral Majority onto his side by going socially conservative, which I don't think he or his party would do.