(CNN) - A new poll in Missouri provides more evidence that President Barack Obama and his administration's agenda are hurting more than helping Democratic candidates running in moderate to conservative states in this year's midterm elections.
The president's approval rating stands at 34 percent in Missouri, according to a new Mason-Dixon survey conducted for the St. Louis Post-Dispatch and KMOV-TV, with 57 percent saying they disapprove of the job Obama's doing in the White House.
The poll, released over the weekend, also indicates that in the battle for Missouri's vacant Senate seat, seven-term Republican Rep. Roy Blunt leads Democratic Secretary of State Robin Carnahan 48 percent to 42 percent, with one in ten likely voters undecided.
Carnahan and Blunt are both expected to easily win their party primary contests, held in eight days. They would then face off in a battle that pits two of the most famous political families in the state against each other. Both candidates are fighting to succeed Republican Sen. Kit Bond, who is not running for re-election this year. The race is one of the few where the Democrats have a chance to pick up a GOP held seat.
Brad Coker, managing director of Mason-Dixon Polling & Research, told the Post-Dispatch that Obama's unpopularity in Missouri was a key reason Blunt was faring better in the Senate battle.
The president visited Missouri earlier this month, for an event on the economy and to headline a fundraiser for Carnahan. It was Obama's fourth trip to Missouri since he narrowly lost the state - by less than 4,000 votes - in the 2008 presidential election to Sen. John McCain.
In March, Republicans pounced on Carnahan when she didn't attend an Obama fundraiser for Sen. Claire McCaskill and a health care reform event in her state, saying she was trying to keep her distance from the president. Carnahan's campaign said she was in the Washington, DC for a conference as part of her duties as secretary of state. Carnahan did team up with Obama when he came back to Missouri a month later to hold an event on the economy.
"He helps with fundraising and, possibly, with turnout, but the single most important reason why Democratic candidates in Democratic and swing states - Ohio, Missouri, Pennsylvania, Wisconsin, Washington and even Illinois - are in trouble is President Obama, and his agenda," says Stuart Rothenberg, editor and publisher of the non-partisan Rothenberg Political Report.
The Mason Dixon poll was conducted July 19-21, with 625 likely voters in Missouri questioned by telephone. The survey's overall sampling error is plus or minus four percentage points.
–Follow Paul Steinhauser on Twitter: @psteinhausercnn