Updated 2:55 p.m. | Missouri Rep. Russ Carnahan filed today to run in the urban St. Louis 1st district, setting off a potentially racially charged Democratic primary with Rep. William Lacy Clay that pits two Missouri political dynasties — one white, one black — against each other.

In the majority-minority district, both Congressmen will be familiar to voters, but Clay probably has the early edge. Only a third of Carnahan’s current constituents were drawn into the reconfigured 1st.

“It’s impossible to overlook the minority aspect here,” said Mike Kelley, a St. Louis Democrat who is a former executive director of the Missouri Democratic Party. “There will be a lot of downticket races that will have primaries, particularly in the African-American community, that will drive some turnout in this election. It will be something Caranhan will have to overcome, and it will be something that Clay will have to capitalize on.”

Carnahan’s current 3rd district was essentially eliminated in redistricting. He’s supported a so-far unsuccessful court battle waged to overturn the lines, but today’s filing appeared to be a partial admission of defeat on the judicial front.

“Based on the maps that exist today, I filed to run in the new St. Louis 1st Congressional District, which merged the core base of my current district in Central and South St Louis into a new district, which includes the entire City of St. Louis along with Central and North St. Louis County,” Carnahan said in a statement.

Carnahan, who is white, said that he believes the map is unconstitutional as drawn and passed by the Republican-controlled Legislature, and that he is holding out hope that the state Supreme Court rules against it. The St. Louis area should have three, not two, districts, he said.

“This would be a more accurate and fair representation of our state and I continue to remain hopeful that the Supreme Court will intercede on behalf of all Missourians,” Carnahan said.

Clay, a member of the Congressional Black Caucus, was bit more direct.

“I am the Democratic incumbent in Missouri 1. I am running for re-election. I will win decisively,” Clay said.

The 1st district is a safe Democratic seat. Whichever Member wins the primary will easily be re-elected in November. There’s the potential that other people could get in the race as well, which would dramatically shift the dynamic of the primary.

“We’re a long way from knowing what this race is going to look like,” Kelley said. “There, potentially, could be other folks who get in this race.”

Whatever the field looks like, politicos in St. Louis expect one of the Members to win. In fact, both factions have been preparing for the potential race for some time.

“Everybody has seen this day coming,” said a St. Louis Democratic source familiar with the political contours of the city. “But the powder’s lit now.”

The source explained that in such a heavily Democratic district, more liberal parts of the electorate would probably decide the race.

“You’ve got two progressive candidates who are going to compete for the progressive vote and I think that’s where this race will actually be tipped,” the source said. One issue that the source thought might help move the needle among that community was emphasizing the rebirth of city. “Being a good cheerleader for St. Louis is going to be a very good way to connect with the younger, more progressive voters,” the source said.

The National Republican Congressional Committee took a victory lap after Carnahan’s filing this morning.

“Left without a home, Carnahan had no place to hide from his years of devastating job-destroying policies and was forced to run-for-cover and primary a fellow Democrat Congressman,” NRCC spokeswoman Andrea Bozek said in a statement. “Nothing about this situation is helpful to Democrats who are already struggling to defend their indefensible job-destroying record to dissatisfied voters throughout the country.”

The Democratic Congressional Campaign Committee knocked Carnahan off its Frontline program, which benefits vulnerable Members, months ago.

In a meeting with reporters this morning, DCCC Chairman Steve Israel (N.Y.) said the party navigates primaries with two Congressman “by taking your hands off.”

He said the committee was “defiantly secular on those Member-to-Member races.”

“The DCCC’s position,” he said, “may the best person win.”