Missouri Republican Roy Blunt has taken his largest lead in a poll since May, leading Democrat Robin Carnahan by 6 points in the race for the state's open Senate seat. Blunt takes 48% to 42% for Carnahan and 10% undecided.

Blunt now leads by 4 points in the RCP Average.

According to the Mason-Dixon poll conducted for the St. Louis Post-Dispatch, both challengers should cruise easily through next week's primaries to officially begin what's expected to be a competitive general election. However, President Obama's standing in the state could portend trouble ahead for Carnahan in a state Obama came 4,000 votes shy of carrying in 2008.

Just 34% approve of the job Obama is doing as president, 12 points below the national average. Even as the president's job approval rating has hovered below 50% for months, his favorable rating -- which takes note of how voters see him personally -- has often remained much higher. But not in Missouri, where just 33% hold a favorable view of Obama.

Blunt will likely open the general election race with more money than Carnahan. As of July 1, Blunt had more than $4.5 million in the bank compared with Carnahan's more than $3.6 million.

The survey of 625 registered voters was conducted July 19-21 with a 4% margin of error.

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