Republican National Committee Chairman Reince Priebus stands onstage at the Republican National Committee's winter meeting Jan. 24, 2014, in Washington, D.C.

Democrats Turn Pessimistic About the Midterms

Former White House press secretary says Senate could fall to GOP.

Republican National Committee Chairman Reince Priebus stands onstage at the Republican National Committee's winter meeting Jan. 24, 2014, in Washington, D.C.

Republican National Committee Chairman Reince Priebus told CNN that the GOP has vastly improved its use of political technologies since Obama won re-election in 2012.

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Democratic strategists are increasingly worried about their party's potential losses in the midterm elections this November, and with good reason.

Robert Gibbs, former White House press secretary for President Barack Obama, added to the chorus of concern when he said the Senate "definitely" could shift to Republican control this fall. The GOP needs to pick up six seats to take a majority. Gibbs said there's no doubt that the faulty rollout of the Affordable Care Act, Obama's signature domestic program, "is still providing a huge hangover" for Democrats. "There's a real, real danger that the Democrats could suffer big losses," Gibbs said.

He added that, if the Republicans take the Senate and maintain control of the House, the last two years of Obama's presidency would be badly damaged. "If we lose the Senate, turn out the lights," Gibbs told NBC Sunday. "The party's over."

[POLLSTERS: Obama's Failures Key to GOP Victory in Midterms]

Gibbs provided a contrast to the relatively upbeat comments of Dan Pfeiffer, a senior White House adviser to Obama, who predicted that the Democrats would retain control of the Senate and said, "The president will be an asset in every way to help these [Democratic] candidates." This will include not only raising money and actively campaigning, Pfeiffer said, but also encouraging Obama strategists to assist Democratic candidates in using the latest campaign technologies such as microtargeting of key voting groups. "This president wrote the book on running and winning modern campaigns," Pfeiffer told NBC. "We're going to take all of our resources and help Democrats up and down the ballot."

But Pfeiffer made the same point that Obama has emphasized in recent weeks: Democratic turnout tends to decline substantially in midterm elections, and this could badly damage Democratic prospects. "Democrats have to do a better job of turning out for midterm elections, " Pfeiffer said. "We're very good in presidential years and less good in midterms. If more Democrats do not turn out, we will not do well."

Reince Priebus, chairman of the Republican National Committee, told CNN that the GOP has vastly improved its use of political technologies since Obama won re-election in 2012. Regarding issues, Priebus added: "Obamacare is complete poison out there in the field."

Political strategists of both major parties said the victory of Republican David Jolly, a former Washington lobbyist, in a special House election in Florida last week was a bad omen for Democrats. Jolly used Obamacare as a bludgeon against his Democratic opponent.

The latest NBC News/Wall Street Journal poll also has intensified Democrats' concerns and boosted Republicans' hopes. Forty-eight percent of voters say they are less likely to vote for a candidate who is a solid supporter of the Obama administration, while only 26 percent say they are more likely to vote for such a candidate.

[READ: What the Special Election Win by David Jolly Really Tells Us About 2014]

Obama's job approval rating has declined to 41 percent, the lowest it has been in the NBC/Journal poll; 54 percent disapprove of his job performance.

A key problem for Democrats is that many of the pivotal Senate contests this fall will be in states that Obama lost in 2012, such as Alaska, Arkansas, Louisiana and North Carolina.