Is there such a thing as a progressive Republican? Is it possible that the party whose right wing reflexively attacks everything prized by progressives could ever change its mind?

A century ago, there indeed were progressive Republicans. They took bold stands against that era’s most powerful corporations and supported many issues that now are associated with the political left: anti-trust policies, workmen’s compenation, child labor laws, minimum wages, maximum workweeks, workplace safety, voter recalls and referendums, Wall St. transparency, graduated income and inheritance taxes, environmental conservation and public disclosure of campaign donations.

How could that be? Unreasonable Men: Theodore Roosevelt and the Republican Rebels Who Created Progressive Politics, by Michael Wolraich, explains it. A little more than a century ago, the nation’s political dynamics were strikingly similar to today—though with different partisan labels—with populist concerns like inequality at center stage.

On one side was entrenched corporate power, represented by one wing of Republicans called the standpatters or Stalwarts. Today, they’d be the GOP’s libertarians or Chamber of Commerce elites. In the party’s center were paternal pragmatists, like Roosevelt when he became president, who was sympathetic to populist goals but felt that doing what was best for the public wasn’t the same as caving to public opinion. On the party’s left, were progressives, epitomized by Wisconsin Gov. and the U.S. Sen. Robert La Follette, who trusted that an informed electorate needed to take back power from the plutocrats.

In those days, the biggest political fights centered on the power and influence of railroads and banks, that era’s economic gatekeepers, because almost all livelihoods were tied to their activities: farmers sending crops to market; manufacturers getting supplies and shipping goods; merchants in downtowns and city centers; everyone getting paid. Starting in Wisconsin, LaFollette called for shipping cost controls, audits of corporate books and more responsive politics. All were very popular with voters.

At first, most of the Republicans in the nation’s capital believed that government’s role was to pass laws backing commerce and get out of the way. Sound familiar? They called La Follette a “Socialist,” an egomaniac, and the most dangerous man in America. He replied that he was the safest man in America, because all that he wanted was for the public’s voice to be heard and heeded by their elected politicians.

Unreasonable Men recounts these struggles and how they unexpectedy evolved into an agenda and legal framework that shaped modern America. When Roosevelt ran for a second full term in 1912 as a third-party candidate—he first became president after William McKinley was assassinated—he had fully embraced the progressive agenda pioneered by LaFollette and by earlier Democrats such as William Jennings Bryant. But like Ross Perot’s 1992 presidential campaign, when that major third-party candidacy cut into Republican votes, Roosevelt lost to Democrat Woodrow Wilson, who quickly took up the mantle of progressive reformer. Like Lyndon Johnson 50 years later, Wilson’s populist achievements were eclipsed by an overseas war, World War I.

The most intriguing parallel from this period is a question that still echoes today—whether progressives should demand big systemic changes or work more gradually within the political system. The answer is surprising. La Follette’s radicalism, which generated vast public support—like Sen. Elizabeth Warren today—did not result in LaFollette getting elected president. But that agenda was soon taken up by others at the highest levels of national politics and swept aside Congress’s corporate defenders and obstructionists.

The book raises other interesting questions for today, as the multi-faceted issue of American inequality is animating the political left, just as the natavist anti-government Tea Party is dominating the right. If history as author Michael Wolraich is a guide, the agenda and policies benefiting the most people will win out, regardless of the partisan labels.

That’s good news for progressives. Of course, we still have to get there—or wait for the pendulum to return in Congress, the White House and federal Courts. But Unreasonable Men offers a good, hopeful read for these politically slow early summer days. And, yes, there once were progressive Republicans.