President Barack Obama's expected nomination of Anthony Foxx as transportation secretary could finally bring some diversity to Obama's Cabinet -- but that it's taken this long underscores the challenges faced by black politicians, experts say. There hasn't been a single African-American elected to the Senate since Obama entered office, and a new generation of young, black politicians have struggled to win races. "We're not there yet," says Rep. John Lewis, D-Ga. "That's why when people ask me whether the election of President Obama is the fulfillment of Dr. King's dream, I say, 'No, it's just a down payment. There's still a lot of work to do.' "