The battle lines have now been clearly drawn between conservatives who want to include the defunding of Planned Parenthood in the upcoming budget fight and  the Republican leadership that wants to separate the issue in order to get a continuing resolution passed.

Democrats have already said they will block any move to defund the group, who have come under withering fire as a result of a series of undercover videos showing them negotiating the sale of fetal body parts.

The battle threatens to shut down the government unless the GOP leadership can work around conservative opposition.

The Hill:

Rep. Mick Mulvaney (R-S.C.), a founding member of the House Freedom Caucus, spearheaded a letter to House GOP leaders shortly before lawmakers' August recess that stated he and 17 other Republicans would not vote for any spending bill that continues funding for Planned Parenthood.

But with Congress set to return to Washington this week, it remains to be seen whether Mulvaney and his allies can gather enough support to force the hand of leadership.

Rep. Diane Black (R-Tenn.), who has written legislation that would freeze Planned Parenthood funding for one year while Congress conducts an investigation into its fetal tissue program, says she doesn’t support using the government funding bill as leverage in the fight.

Black said she has secured a “commitment” from House GOP leadership that her bill will get a floor vote in the coming weeks, according to her spokesman.

“I wholeheartedly agree with the spirit and intent of my friend, Congressman Mulvaney’s letter,” Black said in a statement provided to The Hill. “The sad truth, however, is that President Obama is likely to veto any measure that combats funding of his political allies at Planned Parenthood.”

“I believe we must consider how to most effectively wage this battle while acknowledging our current political realities, positioning our movement for long-term success, and avoiding a government shutdown — which would not defund Planned Parenthood and would only embolden our radically pro-abortion president,” she added.

Mulvaney spokeswoman Stephanie Faile declined to specify the new total number of signatures on the letter, but said a “final count” would likely be released this week.

The letter would likely need to attract far more signatures to pose any real danger to passage of the stopgap funding bill that is expected on the House floor this month. At least one other Republican, Rep. Dave Brat (Va.), has added his signature to the letter over the August recess.

Still, 19 pledges falls short of the maximum number of defections GOP leaders can afford without needing help from Democrats to pass a spending bill. Assuming all 246 House Republicans are present to vote, GOP leaders can lose up to 28 of their members and still pass legislation on their own.

There isn't likely to be a compromise on this issue that would satisfy conservatives, so the GOP leadership is going to have to contain the revolt. In the House, Speaker Boehner won't have a problem sitting on the troublemankers. But 5 or 6 Senators determined to blow up the budget can certainly give Mitch McConnell a headache. He will likely win in the end, but a handful of Senators who use parliamentary manuevers can delay the proceedings.

Unfortunately, for those who wish to withhod the $500 million that Planned Parenthood gets from the government every year, it's hard to envision a legislative path with the current president and congress that would yield success.