The defeat Saturday of Louisiana Democratic Sen. Mary Landrieu was essentially the final act in the Republican Party’s control this fall of the South -- a transition expected to have a significant impact on the 2016 White House races.  

The victory by Republican challenger and Louisiana Rep. Bill Cassidy means that Democrats in January will be left without a single U.S. senator or governor across nine states -- stretching from the Carolinas to Texas.

And GOP runoff victories Saturday in two Louisiana House districts ensure the party of at least 246 seats, the largest Republican advantage since the Truman administration after World War II.

Furthermore, Republicans in Alabama, Arkansas, Georgia, Mississippi, North Carolina, South Carolina, Tennessee and Texas will control nearly every majority-white congressional district and both state legislative chambers.

But will the conservative-leaning voters who appeared this year to have written a closing chapter for the white Southern Democrat have the same impact on the 2016 presidential races?

"The Republican presidential nomination will run through the South," says Ferrell Guillory, a Southern politics expert based at the University of North Carolina. "As Mitt Romney found (in 2012), that...makes it harder to build a national coalition once you are the nominee."

Democrats on Sunday argued that the GOP’s control of the South is not an insurmountable problem for Hillary Clinton, Massachusetts Sen. Elizabeth Warren or any other liberal member of their party who makes a 2016 presidential run.

“Right now, there are really two electorates -- the midterm and the presidential. It’s a different math,” Democratic National Committee spokesman Michael Czin told FoxNews.com, pointing out that voter-turnout within his party is expected to be significantly higher in 2016.

Democratic strategist and pollster Ben Tulchin said the 2008 and 2012 elections prove that “Democrats don’t need the Deep South to win.”

In 1976, former Georgia Gov. Jimmy Carter became one of the last true Southern Democrats to win the White House. He won every Southern state except Oklahoma and Virginia. In 1992 and 1996, Arkansas Gov. Bill Clinton, considered a more conservative Democrat, won only a handful of Southern states in winning the presidency.  

Tulchin also argued a moderate Republican will likely have more problems in 2016 in the Deep South than a liberal Democrat, considering the early South Carolina primary, followed by those in other states across the region, could hurt somebody like New Jersey GOP Gov. Chris Christie.

“His best hope there is the conservative candidates split that vote,” said Tulchin, president of San Francisco-based Tulchin Research.

The region also is home to GOP Sens. Ted Cruz, of Texas, and Kentucky's Rand Paul, both Tea Party favorites and popular presidential hopefuls.

Other Democrats argue that an election without Obama and his widely unpopular agenda in that region also improves their chances.

“The No. 1 thing to be competitive in the South is to have Barack Obama not be president anymore,” North Carolina pollster Tom Jensen, who runs the Democratic firm Public Policy Polling, told Politico. “It’s just a simple reality that Southern whites really, really despise him in a way they have not despised any other president.”

Democrats also argue that changing demographics, such as the growing minority populations in Georgia, North Carolina and Texas, will help.

Louisiana Republican Party Chairman Roger Villere rejects the notion that Southerners could complicate Republican electoral fortunes in the long-term.

"Whether it was the old Southern Democrats or Republicans now, we've pushed the liberal wings of the parties for a long time," he said. "I think it's good for the party and for the country."

The Associated Press contributed to this report.