A looming vulnerability for Sen. Amy Klobuchar as she runs for president is that, unlike Democratic rivals such as Joe Biden or Bernie Sanders, she has not achieved strong support in a key Democratic constituency — African-Americans.

She likes to boast that she runs well in red districts. But as a politician from a Midwestern state that's still by far mostly white, Klobuchar has not until now had to spend a lot of time courting black support.

That could be a potential weakness as the Democratic primaries extend beyond Iowa and New Hampshire, two other states without large minority populations. The issue came into focus last week when several prominent black Democrats in South Carolina criticized Klobuchar in a Bloomberg News story for initially planning to skip a high-profile Martin Luther King Jr. Day event in the Palmetto State.

She then attended after all.

In Iowa on Tuesday, at a news conference by Klobuchar backers in the Legislature, Rep. Ruth Ann Gaines of Des Moines said she believes Klobuchar's support from black Democrats is on the upswing. Gaines, who is black, was the first sitting member of the Iowa Legislature to endorse Klobuchar.

"I think her African-American support is getting stronger; with Sen. [Cory] Booker leaving the race it will be stronger, and with me out there supporting her it will be OK," Gaines said.