The ad buy comes days after polls for the first time showed Democratic Secretary of State Jason Kander leading Sen. Roy Blunt. | Getty GOP spends to shield Blunt from tough challenge

Senate Republicans are moving to aid Missouri GOP Sen. Roy Blunt, placing their first ad reservations and preparing for a seven-figure ad buy, according to a Republican source familiar with the plans.

The National Republican Senatorial Committee placed its first, $270,000 ad buy supporting Blunt in St. Louis, the source said, but more ads are on the way. The ad buy comes just days after independent polling for the first time showed Democratic Secretary of State Jason Kander leading Blunt. Senate Democrats are increasingly shift their sights to Missouri, where they believe Blunt's long time in Congress makes him vulnerable against the 35-year-old Kander, a military veteran.


The Republican source suggested the ads will link Kander to Hillary Clinton, who is losing in Missouri to Donald Trump, according to public polls.

"Voters will be left with no doubt that Jason Kander is a loyal Hillary Clinton partisan," the Republican source said. "Jason Kander would be Hillary Clinton’s senator, not Missouri’s."

Democrats are making a significant investment in Missouri as the battle for the Senate enters crunch time. The Democratic Senatorial Campaign Committee is committing $3.5 million to the state.

"This is just the latest sign that Washington Republicans are worried about losing their favorite senator, Roy Blunt," said Chris Hayden, a spokesman for Kander. "Jason clearly has the momentum in the race."