President Donald Trump’s selection of Judge Brett Kavanaugh as a new Supreme Court nominee last Monday culminates a three-decade project unparalleled in American history to install a reliable conservative majority on the nation’s highest tribunal, one that could shape the direction of the law for years to come.

“They’ve been pushing back for 30 years, and, obviously, the announcement is a big step in the right direction,” said Curt Levey, president of the Committee for Justice, a conservative activist group that’s been working toward this goal full time since 2005. “It’ll be the first time we can really say we have a conservative court, really the first time since the 1930s.”

This presumes that Trump can push Kavanaugh through a closely divided Senate heading into a midterm election season, hardly a given. More so than any nomination in a dozen years, Trump’s choice of a successor for Justice Anthony M. Kennedy, the influential swing vote retiring at the end of the month, holds the potential of changing the balance of power rather than simply replacing a like-minded justice with a younger version.

But if the president succeeds in confirming his selection, the new justice is expected to join Chief Justice John G. Roberts Jr. and Justices Clarence Thomas, Samuel A. Alito Jr. and Neil M. Gorsuch in forming a much more consistently conservative majority than before.

That has not happened by accident. A network of activists and organizations has worked assiduously since the 1980s to reach this point, determined to avoid the disappointment they felt after Republican appointees like Earl Warren, William J. Brennan Jr., David H. Souter, Sandra Day O’Connor and Kennedy proved more moderate or liberal once they joined the court.