The predictable response from Democrats will be that Mr. Ryan couldn’t square his principles with the reality of Mr. Trump’s presidency. That might score a quick rhetorical win, but it misses the bigger political picture. America is in the midst of a major political realignment that is redefining both the left and the right. Mr. Trump’s sudden ascendance to power is a symptom of the larger trend and also a catalyst for the intellectual and political reformation that is currently underway on the right, which has led to the announced departures of standard bearers of the ancien régime like Senator Jeff Flake, Senator Bob Corker and now Mr. Ryan.

The job for House Republicans will be to select a new leader who isn’t just more of the same. The last effective leader was Newt Gingrich. Since he stepped down in 1999, Republican leadership has been either corrupt or incompetent. Tom DeLay was indicted (although he was eventually acquitted); Dennis Hastert is a convicted felon. John Boehner was a do-nothing placeholder who now works for a marijuana company; and Eric Cantor so infuriated his own constituents that he was defeated by an underfunded economics professor who still holds the seat. What we need is a clean break with the time-markers and careerists who are content being the party of no.

Mr. Ryan came up under the Boehner-Cantor regime, and their sensibilities have stayed with him. Like them, he failed to advocate — let alone pass — legislation supporting the agenda he claimed to believe in. His coda will be the omnibus spending bill passed last month. Not only did the bill fund Democratic priorities, and not fund Mr. Trump’s border wall, it also made the wall’s construction illegal on a stretch of the Texas-Mexico border that is home to the federally owned Santa Ana Wildlife Refuge.

Mr. Ryan’s legacy will be one of lost opportunities and youthful promise unfulfilled. He’s left a mess that his successor will have to clean up. House Republicans under Mr. Ryan became a disorganized rabble rather than the energetic and effective conference confidently enacting the agenda that one would expect from a party that controls both houses of Congress and the presidency.

Republicans need a leader who is in step with the president and his agenda, one who emphasizes pro-citizen immigration policies, pro-worker economic policies and an America First national security policy that is circumspect about foreign military intervention.

Equally important, the next leader must be someone who commands the respect and obedience of the conference. Voters gave Republicans power because they believed that the policies the party promised offered them a better future. Republicans must repay that trust with action. Just as Moses couldn’t enter the promised land because he had broken faith with God, much of the current House leadership has broken faith with its voters. House Republicans need to find their Joshua — a leader who sees the party’s future and can bring its members together to build it. Ambitious politicians are always willing, but who’s ready?