Thomas Balcerski teaches American history at Eastern Connecticut State University. He is the author of "Bosom Friends: The Intimate World of James Buchanan and William Rufus King" (Oxford University Press). He tweets @tbalcerski. The opinions expressed in this commentary are his own. Read more opinion at CNN.

(CNN) Once more, the upcoming Democratic debates will offer voters a chance to see the party's presidential hopefuls in action. Divisions over ideology and identity have defined the race: the liberals debate the moderates over policy questions, the Northeasterners quibble with the Midwesterners about attracting voters, and the young needle the old over who should lead. The one thing on which the Democratic field seems to agree is that their party fundamentally differs from the politics and policies of Donald Trump.

Thomas Balcerski

By adopting a defeat-Trump-at-any-cost strategy, the Democrats have missed a key lesson from the past: being the party of opposition and the promoters of mere change will only carry you so far. The approach may yield electoral success in the short-term, but it fails to create lasting change and, worse still, does nothing to communicate an effective vision for the future of this country to the voting public. By not recognizing that their enemy is not so much Donald Trump as their own myopic commitment to defining themselves in opposition to him, Democrats risk the future of the country with their lack of vision.

Here is where history can help. By studying the campaign messaging and strategies from prior presidential elections, the Democrats can help to clarify what has worked well and what has failed miserably in the past. As it turns out, the history of the Democratic Party is chock full of examples of both.

During the Great Depression, the Democrats seized power under the charismatic leadership of Franklin Delano Roosevelt. In the election of 1932, Roosevelt ran less against the incumbent, Herbert Hoover, than he did for a program of visionary transformation of America. During the campaign, Hoover attempted to brand Roosevelt as a radical; rather than issuing a direct rebuttal to these attacks, FDR instead rejected the idea that the ongoing economic downturn could not be corrected. This did not prevent Roosevelt from drawing a contrast between his policy ideas and those of the incumbent: "Here is the difference between the President and myself," he declared , "I go on to pledge action to make things better."

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Dubbed the "New Deal," Roosevelt's vision effectively set the political agenda for a generation of American politics. Harry Truman looked to expand the reach of the New Deal with a "Fair Deal" that promised progress in the areas of civil rights, education, health care, welfare, and more. Although he did not fulfill all its stated aims, Truman set the tone for later presidents: Both John F. Kennedy's "New Frontier" and Lyndon Johnson's "Great Society" programs set forth the idea of a safer, more inclusive America that would be more humane to its citizens. These Democrats stood for a vision of America that included government as a partner and not simply against their opponents.

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