Asked during a January debate why he trailed Hillary Clinton so badly among minority voters, Senator Bernie Sanders said he would gain ground once those voters became familiar with his track record and agenda on the economy and criminal justice.

Two months later and on the eve of another important primary voting day, Mr. Sanders remains on the wrong side of a yawning gap among African-Americans even as his performance among whites has been impressive.

One important reason for this may be that African-Americans have experienced somewhat more favorable economic trends in recent years. While still worse off than whites, African-Americans have seen their jobless rate fall a little further than whites have, relative to a prerecession average. Furthermore, the decline has been faster for African-Americans in the last year.

The economist Robert J. Shapiro recently measured the income growth that people experience as they age. He found that, on average in 2013 and 2014 (the most recent data available), incomes for blacks in their 30s, 40s and 50s grew more rapidly than for whites in the same age group. Older people, who strongly support Mrs. Clinton, have also seen income gains relative to other groups since the recession.