To date, our politics hasn’t met the challenge. President Trump and the Republican Party have responded with an unworkable model: tamping down the political power of emerging populations, stirring anxiety among white Americans and shutting down borders. The multiracial reality is that even when minorities become a majority, they still often lose.

Democrats have made more efforts than Republicans to change this reality, but there’s room for improvement. The candidates at the debate on Thursday should examine the role racism plays in the disparities in income and education that exist for blacks and Latinos even in progressive and majority-nonwhite states like California. They should respond to the low turnout of Latino and Asian voters nationwide, and their dismal share of elected positions. And they should take the opportunity to take a hard look at Texas, where protracted struggles over power have played out in lawsuits over discriminatory voter identification laws, overly aggressive voter purges and gerrymandering that denies fair legislative and congressional maps to the state’s large nonwhite communities.

There is one other promising path, and I saw it in Houston. As a reporter in that city 20 years ago, I observed a model for avoiding the zero-sum game that some politicians depict to frighten audiences and to win votes.

I profiled three businessmen — a black architect, a Latino engineer and a white construction contractor — who had joined forces to help elect Houston’s first black mayor, Lee P. Brown. Even then, no single racial group held a majority in the city, and the businessmen put race aside to come together for mutual benefit. They saw what could be gained by pooling their money and political clout behind the same candidate — in their case, the city building contracts they hoped would come their way if they backed a winner.

Theirs was a pragmatic calculation; they weren’t close friends. The white businessman, Richard Lewis, who owned a construction company, described himself a “Republican from the womb.” Mr. Lewis told me he fell behind Mr. Brown, a Democrat who supported affirmative action, because the city’s demographics, with its black-Latino combined majority, made it clear that a Republican could not win.