Reagan would have been an obscure Senator and he would have been defeated for re-election in 1974.
Why was Reagan a big deal? He was a big deal because he was Governor of California since 1966. The timing is crucial; his 1966 election enabled him to put on a last minute candidacy for President in 1968 (after months of conservatives wishing he'd put his hat in the ring). He was re-elected in 1970 by avoiding the cultural issues and the Vietnam War issue because he was Governor. Let's not forget that in 1968 and 1970 California rejected hawkish Republicans for dovish Democrats in their US Senate races. A non-incumbent Reagan would have lost both races.
The key for Reagan to be a viable Presidential candidate was his 1966 Gubenatorial win. Reagan didn't run for the Senate in 1974 because at that time he was considered unelectable in California. His Presidential campaigns rehabilitated his image with the home folks, as did the ebbing of the Vietnam War and the cultural/countercultural issues surrounding it.
The Reagan you created would not have won the primary against Ford in 1976. But let's say that he had. If that were the case, he'd have been pigeonholed as a reactionary Senator with a voting record to support the label and he'd have lost in a landslide to Carter; the reasonable moderate versus the dangerous kook. Reagan beat Carter because the path he took enabled him to avoid being pigeonholed and because it was the incompetent Carter, and not the moderate and reasonable Carter that Reagan ran against in 1980.
Uh, I think you misread the thing, it has Reagan remaining a Liberal Democrat and facing Carter in the general. But on the scenario, I think Reagan beats him handidly. Another interesting scenario is a Speaker of the House Ronald Reagan facing Nelson Rockefeller.
