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Trueman - had a partial term after FDR died, won in 1948 but lost in 1952.

In reality, Truman had essentially two terms in office - under the 22nd Amendment he wouldn't have been qualified to run for reelection in 1952, if not for the clause in it which grandfathered him into eligibility.
No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of the President more than once. But this Article shall not apply to any person holding the office of President, when this Article was proposed by the Congress, and shall not prevent any person who may be holding the office of President, or acting as President, during the term within which this Article becomes operative from holding the office of President or acting as President during the remainder of such term.
And in fact Truman did not run in 1952; Eisenhower defeated Adlai Stevenson in that year.

And, in a counterfactual, Kennedy would almost certainly have won reelection in 1964 had he not been shot. Johnson's election could be counted as a second term for Kennedy much as GHWB's election was a "third Reagan election."
Those two cases water down your thesis somewhat - but the point remains that since 1950 no Democrat president has been able to defend what it pleases them to call "liberalism" in a presidential election after having modeled it in the White House for four years. And indeed, they inverted the meaning of "liberalism" in the 1920s to make it a euphemism for socialism.