Sen. Bernie Sanders (I-Vt.) once told a fellow left-wing activist that the Democratic Party was too intellectually bankrupt to allow the progressive movement to flourish within it.

In a 1985 letter newly obtained by HuffPost in which Sanders debated running for governor, he wrote: Whether I run for governor or not is really not important. What would be a tragedy, however, is for people with a radical vision to fall into the pathetic camp of the intellectually bankrupt Democratic Party.

Times have changed.

Sanders, who has served as an independent in Congress first in the House and now in the Senate since 1991, is now among the leading Democratic candidates for president, second behind former Vice President Joe Biden in national polls, and tied for first in Iowa. Hes raised more money than any other candidate in the Democratic primary, with more individual contributions. His platform which includes Medicare for All, tuition-free college, and wealth redistribution through aggressive taxes on the richest Americans defines the partys progressive wing.

He has taken the Democratic Partys loyalty pledge and repeatedly promised to support whoever becomes the party nominee to defeat President Donald Trump. But that hasnt been enough for many of his critics in the partys establishment, who are likely to point to the letter as evidence he doesnt play nice with the party.

At the start of his career in politics, Sanders viewed the Democratic Party as hopeless. By 1985, he had already made several failed bids for elected office in Vermont as a member of the progressive Liberty Union party. He finally succeeded in 1981, becoming mayor of Burlington, the states largest city, and toppling a five-term Democratic mayor.

At the beginning, the Democrats were very angry with him, Jane Sanders, Sanders wife, said in an interview with HuffPost. Burlingtons Board of Aldermen a part-time, 13-seat city council resisted Sanders efforts. They wouldnt let him appoint any of the mayoral appointments. They stopped him from hiring the city attorney, city clerk, city treasure ... [The Democrats] were outright enemies in the beginning.

Sanders never won full control of city government, but he organized enough voters to elect some allies onto the board and win veto power. He soon became popular enough to win reelection by a 20-point margin.

The Sept. 5, 1985 letter which has not previously been reported on came as Sanders was considering a run for governor, and left-wing activists in the state and around the country were debating whether he should mount an independent bid or launch a primary challenge to the states Democratic governor, Madeleine Kunin.