Former President Barack Obama's endorsements so far this campaign season include Democratic candidates for governor and lieutenant governor in Florida and Georgia and about a half dozen congressional hopefuls in Texas.

But noticeably absent from the more than 340 political candidates receiving Obama's endorsement are politicians running races in conservative states the former president lost in the 2008 and 2012 presidential elections: Alabama, Mississippi, Louisiana, Tennessee, Arkansas, Kentucky and South Carolina.

"Some candidates may feel that an endorsement by former President Obama is kryptonite," said Derryn Moten, chairman of the history and political science departments at Alabama State University

Victories in the South, observers say, will be difficult for Obama to find.

"Like the national Democratic Party, I suspect that Obama would prefer not to waste his endorsements on candidates that have virtually no chance of winning," said Richard Fording, a political science professor at the University of Alabama.

"The fact that Obama has yet to endorse candidates from Alabama is somewhat disappointing for Democrats in this state, I am sure," he added.

Democratic strategy

In Alabama, the highest profile race on the November 6 ballot is for governor where Tuscaloosa Mayor Walt Maddox is the Democrat facing Republican Gov. Kay Ivey.

Maddox's campaign spokesman said this week that he has not sought out-of-state endorsements.

It's somewhat similar to the campaign tactic that Democratic U.S. Senator Doug Jones utilized last year leading up to his surprising victory in Alabama's special Senate election over Republican Roy Moore.

Jones did receive political help from national figures like former Vice President Joe Biden and Georgia Congressman John Lewis. But Obama, former Democratic presidential candidate Hillary Clinton, and a host of other prominent national Democrats stayed out of Alabama during the weeks and months leading up to Election Day.

New Jersey Democratic Senator Cory Booker, a potential 2020 presidential hopeful, did campaign with Jones during the final weekend before the election.

"The ones who showed up, thankfully, they were virtually unknown for the people in the state, like Senator Cory Booker, so he didn't damage Doug Jones by stumping for him," said Moten. "But if Mrs. Clinton had showed up, my goodness, it would've been a circus."

Trump endorsements

Endorsements from political stars, such as sitting or former presidents, can be a touchy subject in Alabama no matter which party is involved.

President Donald Trump, who enjoys some of his most favorable polling in Alabama, endorsed two Republicans last year during the special Senate election contests.

Both of those candidates - Luther Strange during the Sept. 27 GOP runoff, and Roy Moore during the general election - lost their respective races.

Angi Stalnaker, a Republican strategist based in Montgomery, said that national endorsements "of any kind" have little impact in the South.

"In the South, we just don't like to be told who to vote for," said Stalnaker. "You compound that when you take someone who is unpopular in the area and the Obama team is smart enough to know that an endorsement in the South (isn't helpful)."

She added, "Generally speaking, if you have a governor or presidential endorsement, they tend not to do well here in Alabama historically."

Texas absence

Obama is backing two black Democratic hopefuls for governor, one in Georgia (Stacey Abrams) and another in Florida (Andrew Gillum). He's also pushing for U.S. Senator Bill Nelson, who is running for re-election against Republican Florida Gov. Rick Scott.

The former president is notably absent from a widely watched Texas Senate race pitting Democrat Beto O'Rourke against incumbent Republican Senator Ted Cruz.

O'Rourke has been compared to Obama in terms of energizing the Democratic base and drawing large crowds to campaign events.

But O'Rourke, in recent media interviews, said he was "not interested" in the former president's endorsement. He also said that he has not sought it.

Obama has delivered 11 endorsements to various Democratic candidates in Texas.

"In most races where Obama is endorsing, they are purple districts where Democrats are concentrating on," said Cal Jillson, a political science professor at Southern Methodist University in Dallas. "The U.S. House races and the Texas statehouse races, and those around the country and those in southern states are where Obama thinks he can play to a good effect."

Said Jillson: "O'Rourke is doing well on his own."

'Detrimental'

In Tennessee, the president is absent from the state's hot Senate contest between Republican Rep. Marsha Blackburn and Democrat Phil Bredesen.

That race has drawn some unexpected national attention from celebrities, such as pop superstar Taylor Swift, who took to social media and endorsed Bredesen.

Bruce Oppenheimer, professor of public policy and education at Vanderbilt University, said he believes three things are governing Obama's endorsement choices this fall:

His endorsement in a close contest can impact outcome

The former president is endorsing candidates with a progressive

No endorsement will be made in a race where the ex-president isn't wanted or where "it might be detrimental to the candidate."

Said Oppenheimer: "So a combination of those factors may limit the endorsements he'll make in some southern states, especially in statewide contests. It is important to note, however, he's making endorsements in a serial manner and not in one big announcement because he likely wants to maximize the attention each endorsement receives."

If another round of endorsements is coming, Fording isn't counting on any benefiting an Alabama Democrat.

"If you look at the states where Obama has focused his endorsements, they generally track with the states that are being targeted by the major national party campaign committees," said Fording.

He added, "The politics of political endorsements are tricky. Because Obama is still a very polarizing figure, he must consider whether his endorsement will help mobilize the opposition and perhaps even have the net effect of hurting his preferred candidate."