I imagine a great deal of people would be turned off by their hawkish views right after Vietnam, which could lead to a substantial decrease in voter turnout and an increase in distaste towards then-contemporary politicians. Their debates would largely be focused on domestic affairs as their foreign policy views were both very hawkish and the campaign would be more or less concentrated on the economy and government as in OTL. Reagan could pull a Washington outsider style campaign (Similar to Carter) better than Jackson due to Jackson being a longtime Senator, but Reagan would also have to spend much of his time quashing the inevitable divisions in his party and that could dampen his campaign. I'm still betting Reagan would lose due to the previous years of Watergate, Stagflation and resignation defining the Republican Party of the past 8 years as well as due to voter fatigue, which could repudiate the ascendant hard Right Wing faction of the Republican Party in favor of more moderate elements. I would give Jackson a narrow advantage that could widen if he goes full left-wing populist on matters of healthcare and moderate on civil rights issues and uses those to paint Reagan as a Right-Wing extremist. Reagan could win, but I doubt he would in in 1980 as voter fatigue only increases and he simply won't have the same support in Congress like in the 80's to go for full on Reaganomics, leading to a watered down "recovery" (Or the economy goes further down the tubes) and he would lose decisively in 1980. If Jackson wins, than that's where things get more interesting in regards to the post-Vietnam military, if UHC or the ERA get passed and if he can heal the economy. I also doubt SALT II would occur as Jackson opposed it in OTL. Another question is if he will even survive a hypothetical second term as well due to his death in 1983 OTL.