Last week was momentous for President Joe Biden's party, and perhaps for the Republican Party. Without apparent qualms, Biden sided with progressives who demand that the $1 trillion actual infrastructure bill (roads and similar stuff) should not be voted on in the House until the Senate passes the "soft infrastructure" bill.

According to progressives' Rumpelstiltskin spin-straw-into-gold economics, this bill will cost only $3.5 trillion. Or plausible calculations say perhaps $5 trillion. The bill includes tax credits for purchasers of electric bicycles, and almost everything else imaginable, except actual infrastructure.

By siding with progressives, Biden — an open book who has been reading himself to the nation since he arrived in the Senate 48 years ago — showed, again, that he is not (as Otto von Bismarck said of Louis-Napoleon) "a sphinx without a riddle." Neither is Biden a progressive. He is a party man who goes where it goes.

History is propelled by intense, idea-driven minorities. (As 1917 dawned, there were 24,000 Bolsheviks in the Russian Empire's population of roughly 125 million.) Progressives today have intensity because they have two ideas: "equity," meaning the elimination of disparate outcomes produced, progressives say, by sacrificing "social justice" on the altar of equality of opportunity, a chimera; and "proper equality," understood as ever-more-equal dependency of ever-more people on government.

Biden is today's Prince Felix Schwarzenberg, the Austrian prime minister who, when asked about his nation's moral debt to Russia for its help in crushing an 1848 revolution, replied: "Austria will astound the world with the magnitude of her ingratitude."

In the competition for the Democrats' 2020 presidential nomination, Americans who voted for Sens. Elizabeth Warren (Mass.) or Bernie Sanders (Vt.) made up approximately one-third of primary participants. The Democrats' moderate majority may be astounded by the magnitude of Biden's ingratitude.

Biden probably chose to align with progressives last week because, preferring their agenda to any presidential preference for splitting differences, they gave him no choice. The Great American Songbook teaches that when an immovable object meets an irresistible force, something's gotta give. It was exhilarating last Friday when the Congressional Progressive Caucus proved to be more immovable than the president's pleas, if any, for compromise with the moderates were irresistible.

The nearly 100-member caucus is wrong about all matters of public policy, but its obduracy is constitutionally wholesome. It is evidence that the sainted James Madison's expectation has not been entirely nullified by party allegiances.

Immediately after the Constitution was ratified, something occurred that the Framers neither desired nor anticipated: the emergence in the 1790s of a party system. By now, this system has attenuated the Madisonian assumption that the houses of Congress would be rivalrous regarding each other, and that Congress itself would jealously husband its power and dignity against diminishment by presidential aggrandizement.

In Federalist 51, Madison anticipated constant constructive tension between the two political branches: "Ambition must be made to counteract ambition. The interest of the man must be connected with the constitutional rights of the place."

Although Madison quickly became, with his boon companion Thomas Jefferson, a creator of what is now the world's oldest political party, he could not have anticipated what would now appall him: the common attitude in Congress that members are mere spear carriers in a presidential opera.

In 2018, a congressman said in defense of a fellow Republican, a committee chairman accused of excessive subservience to the president: "You have to keep in mind who he works for. He works for the president and answers to the president." Such thinking is the principal reason modern presidents are so rampant, and the one reason the Congressional Progressive Caucus is, despite its ideological intoxication, somewhat wholesome.

If the caucus accepts this compliment, it should send a similar salute across the barricades to the two Democratic senators the caucus currently despises. There is an adjective to describe West Virginia's Joe Manchin III and Arizona's Kyrsten Sinema as they resist pressures to buckle — pressures from Biden, the other side of the Capitol, and the great and the good in the media. The adjective is: senatorial.

Originally insulated from gusts of public opinion by state legislatures selecting them, senators are still somewhat insulated by six-year terms. Ideally, there should always be a few senators irritating their party.

Congressional Republicans, quaking in terror of possible disapproval emanating from a pouting former president, should profit from the Congressional Progressive Caucus's example of sturdy independence. And from the caucus's demonstration of what is indispensable to independence: ideas that pull a party up from subservience to a president.

George Will's email address is georgewill@washpost.com.