On Monday, America will observe both the birth of the Rev. Dr. Martin Luther King Jr., whose vision of pluralism, democracy and racial justice made him the most revered civil rights leader of the last century, and the return to office of President-elect Donald J. Trump.

The convergence of Martin Luther King Day and Mr. Trump’s inauguration will be celebrated by some; after all, Mr. Trump’s stunning political comeback was boosted by remarkable gains with voters of color. It will sit uneasily with others, who see Mr. Trump’s movement — fueled by nativism and a rejection of inclusion as a societal aim — as a backlash to many of the precepts central to Dr. King’s philosophy.

But for many, the unusual coupling — only Bill Clinton’s second inauguration on Jan. 20, 1997, coincided with the King holiday — may be a moment of reckoning for a country that has struggled since its inception between its ideals of equality and its divisions over race and ethnicity.

“It’s almost a Godsend,” said the Rev. Dr. William J. Barber II, who will mark M.L.K. Day from the pulpit of Ebenezer Baptist Church in Atlanta, where Dr. King once preached. “There can be a juxtapositioning of vision.”

The convergence of celebrations comes at a crucial time for Black leadership and its historical alliance with the Democratic Party, which Mr. Trump appears to be cleaving. The country is more culturally and racially diverse than in Dr. King’s day, and the marking of what would have been his 96th birthday (on Jan. 15) comes as Black voters are questioning what Black leadership should look like in the second part of the Trump era, amid the country’s disenchantment with policies that are ostensibly meant to address racial disparities.

Americans had an opportunity to elect a Black woman to the presidency for the first time. They pointedly chose not to.

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