I keep hearing that Joe Biden will govern from the “center.” He has no choice, they say, because he’ll have razor-thin majorities in Congress and the Republican Party has moved to the right.

Rubbish. I’ve served several Democratic presidents who have needed Republican votes. But the Republicans now in Congress are nothing like those I’ve dealt with. Most of today’s GOP live in a parallel universe. There’s no “center” between the reality-based world and theirs.

Last week, fully 95% of House Republicans voted against impeaching Mr. Trump for inciting insurrection, even after his attempted coup threatened their very lives.

The week before, immediately following the raid on the U.S. Capitol, more than 100 House Republicans and several Republican senators objected to the certification of electoral results in two states on the basis of Mr. Trump’s lies about widespread election fraud — lies rejected by 60 federal judges as well as Mr. Trump’s own Justice Department and Department of Homeland Security.

Prior to the raid, several Republican members of Congress repeated those lies on television and Twitter and at “Stop the Steal” events — encouraging Trump followers to “fight for America” and start “kicking ass.”

This is the culmination of the growing insanity of the GOP over the last four years. Mr. Trump has remade the Republican Party into a white supremacist cult living within a counter-factual wonderland of lies and conspiracies.

According to various surveys, more than half of Republican voters — almost 40 million people — either believe Mr. Trump won the 2020 race or aren’t sure who won; 45% support the storming of the Capitol; 57% say he should be the Republican candidate in 2024.

In this hermetically sealed cosmos, most Republicans believe Black Lives Matter protesters are violent, immigrants are dangerous and climate change doesn’t pose a threat. A growing fringe openly talks of redressing grievances through violence, including QAnon conspiracy theorists (of whom two are newly elected to Congress), who think Democrats are running a global child sex-trafficking operation.

How can President Biden possibly be a “centrist” in this new political world?

There is no middle ground between lies and facts. There is no halfway point between civil discourse and violence. There is no midrange between democracy and fascism.

President Biden must boldly and unreservedly speak truth, refuse to compromise with violent Trumpism, and ceaselessly fight for democracy and inclusion.

Speaking truth means responding to the world as it is and denouncing the poisonous deceptions engulfing the right. It means repudiating false equivalences and “both sides-ism” that gives equal weight to Trumpery and truth. It means protecting and advancing science, standing on the side of logic, calling out deceit, and impugning baseless conspiracy theories and those who abet them.

Refusing to compromise with violent Trumpism means renouncing the lawlessness of Mr. Trump and his enablers and punishing all who looted the public trust. It means convicting Mr. Trump of impeachable offenses and ensuring that he can never again hold public office — not as a “distraction” from President Biden’s agenda but as a central means of reestablishing civility, which must be a cornerstone of that agenda.

Strengthening democracy means getting big money out of politics, strengthening voting rights and fighting voter suppression in all its forms.

It means boldly advancing the needs of average people over the plutocrats and oligarchs, of the white working class as well as Black and Latino people. It means embracing the ongoing struggle for racial justice and the struggle of blue-collar workers whose fortunes have been declining for decades.

The moment calls for public investment on a scale far greater than necessary for COVID-19 relief or “stimulus” — large enough to begin the restructuring of the economy. America needs to create a vast number of new jobs leading to higher wages, reversing racial exclusion as well as the downward trajectory of Americans whose anger and resentment Mr. Trump cynically exploited.

This would include universal early childhood education, universal access to the internet, world-class schools and public universities accessible to all. It would mean converting to solar and wind energy and making America’s entire stock of housing and commercial buildings carbon neutral. It would mean investing in basic research — the gateway to the technologies of the future as well as national security — along with public health and universal health care.

It is not a question of affordability. Such an agenda won’t burden future generations. It will reduce the burden on future generations.

It is a question of political will. It requires a recognition that there is no longer a “center” but a future based either on lies, violence and authoritarianism or on unyielding truth, unshakable civility and radical inclusion. And it requires a passionate, uncompromising commitment to the latter.

Robert B. Reich, former U.S. Secretary of Labor, is professor of public policy at the University of California at Berkeley and the author of “The System: Who Rigged It, How We Fix It.” Twitter: @RBReich.