No, I'm afraid not. Your opinion of Mondale is skewed by his 1984 run, as is your characterization of him (he was never an "ultra liberal" nor by any stretch of the imagination a "leftist"). Besides which, the electorate was much less conservative in 1976, and Ford's popularity was pretty low. In fact, I think Mondale may well have won in 1976 (he thought about running for the nomination that year, incidentally, but decided against it before any of the primaries started); '76 was a very favorable year for the Democrats. They had made big gains in Congress in '74, and I've always thought that just about any Democratic candidate would have won that year, most of them by a larger margin than Carter did.
Sorry to have to correct you, but there is no doubt that Mondale was an old line tax and spend liberal, even going so far in his 1984 acceptance speech at the Democratic National Conventiion to state that he would raise taxes if necessary.
Mondale was a well known member of the liberal establishment during his two terms in the Senate, long before his well deserved 1984 drubbing by Reagan. Mondale was an avid proponent of the theory that government power and spending could correct social inequalities.
Mondale also showed his complete inadequacy for national office with the first major decision he had to make as a national candidate, his selection of Geraldine Farraro, a complete token candidate, for Vice President.