Washington CNN  — 

The campaign arm for Senate Democrats is targeting nine Republicans up for re-election with a five-figure ad buy because they think that the incumbents are vulnerable on the issue of defunding Planned Parenthood, CNN has learned.

The ads ask whether the senators – eight of whom voted last month to block federal funds to the organization because it performs abortions – were willing to back calls from the right flank of the GOP to shut down the government over the issue. Several of the senators are moderate and most come from states that have a history of electing both Republicans and Democrats.

Republicans currently hold 54 Senate seats and Democrats 46. But in their campaign to hold the Senate, Republicans must defend 24 open seats while Democrats have to protect just 10.

The issue of defunding Planned Parenthood took on new urgency after undercover, heavily edited videos from anti-abortion rights activists appeared to show Planned Parenthood workers discussing the sale of fetal tissue from abortions for scientific research.

A CNN poll released last week shows why Democrats think the issue will resonate. The poll found that 71% of all responders believe it’s more important to fund the government that to strip federal funds from Planned Parenthood. Importantly, for anyone running an election in a highly competitive state, 74% of independent voters say the government should not be shut down over the issue.

Sen. Pat Toomey of Pennsylvania is a main target of the ads because Democrats believe they have a good chance to knock off the Republican who is seeking a second term. Democrats suggest Toomey and other targeted Republicans might “flip flop” on the issue to placate swing voters in their states.

“As a potential shutdown creeps closer, we will see if Sen. Toomey sticks with his votes to defund Planned Parenthood or if he is so scared about his re-election that he flip-flops in a panic,” said Sadie Weiner, spokeswoman for Democratic Senatorial Campaign Committee, in a statement. “These ads will highlight that Sen. Toomey and extremists in Congress are playing a dangerous game, and Pennsylvania families deserve better.”

Toomey’s office did not respond to a request for comment about the ad.

Other senators who are the focus of the ads, which will appear of Facebook and Twitter, are Sen. Rob Portman of Ohio, Sen. Richard Burr of North Carolina, Sen. Ron Johnson of Wisconsin, Sen. Roy Blunt of Missouri, Sen. John McCain of Arizona, Sen. Rand Paul of Kentucky, Sen. Mark Kirk of Illinois and Sen. Kelly Ayotte of New Hampshire.

Ayotte has already stated she is wary of shuttering the government over the funding fight because right now opponents of Planned Parenthood don’t have the votes to be successful.

Ayotte wrote a letter last week to Sen. Ted Cruz, R-Texas, a presidential candidate, who is advocating for the Congress to close the government if it can’t block federal dollars to Planned Parenthood. In it, she questioned the wisdom of such a move since the vote last month to defund the organization got only 53 votes, seven votes shy of what is needed to pass a bill in the Senate and 14 votes shy of the votes needed to override a promised presidential veto of that legislation.

“Given the challenges and threats we face at home and abroad, I oppose risking a government shutdown, particularly when it appears there is no chance of achieving a successful result,” Ayotte’s letter said.

Ayotte’s office reiterated that she opposes a shutdown Monday.

“As a leader who was widely credited with helping bring both parties together to end the last government shutdown, Senator Ayotte strongly opposes shutting down the government and she is fighting against this flawed strategy,” said Ayotte spokeswoman Liz Johnson in a statement.

The campaign manager for Portman also said the senator was working to avoid a shut down.

“Rob has said repeatedly, he will continue to be strongly supportive of defunding Planned Parenthood but he doesn’t support government shutdowns and thinks it can be avoided,” said Corry Bliss.

Even Senate Majority Leader Mitch McConnell, who is working to fund the government, called the effort to defund the organization futile.

Kirk is the only senator who is a target of the DSCC ad who did not vote for the Planned Parenthood defunding bill last month.

CNN’s Manu Raju contributed to this report.