The chairman of the Senate Homeland Security Committee says he wants to clear postal legislation out of his panel in January after delaying a mark up three times in recent weeks.

Sen. Tom Carper (D-Del.) says he and the panel’s top Republican, Sen. Tom Coburn (Okla.), have used the delays to shore up their bipartisan postal proposal.

{mosads}Carper said he wants to meet with committee members on the legislation next month and then schedule a fourth markup — one he’s more confident the committee will be able to follow through on.

“I think we’re making progress there,” Carper told The Hill on Friday.

Still, Carper and Coburn have acknowledged the challenges in getting postal legislation not only through their committee, but past the Senate and eventually to the president’s desk.{mosads}

Lawmakers and outside groups are split on a string of complicated issues, including whether the U.S. Postal Service should reduce six-day delivery, the agency’s healthcare costs and whether to raise prices for sending letters or packages.

Carper and Coburn are also trying to move forward with their plan at a time when the partisan divide in the Senate is even starker than usual, following the Democrats’ invoking of the “nuclear option” to ease the passage of nominees.

“People who support the mailers don’t want to raise prices. People who support the unions don’t want to cut costs,” Coburn said. “You can’t solve it unless you solve it, which means everybody’s got to take some pain.”

Democrats on the Homeland Security Committee, mostly from rural, red states, have already raised a host of concerns about the bill crafted by Carper and Coburn, which would open the door to slower delivery standards.

More liberal Democrats, in fact, complained from the moment that Coburn and Carper dropped the bill in August that the measure wasn’t as strong as the postal legislation the Senate passed in 2012.

“There’s still some issues that have to be ironed out,” Coburn said.

“If you move the bill too far, you won’t have any members on my side voting for it,” the Oklahoma Republican added, noting the complaints from the other side of the aisle. “So, you got to find the sweet spot. It’s difficult.”

Plus, some postal unions are taking even more of a hard line against ending Saturday delivery after the USPS lost $5 billion in fiscal 2013, less red ink than expected.

Those officials say Congress could put the agency on firm ground by eliminating a requirement that the agency prepay for future retirees’ healthcare.

But Postmaster General Patrick Donahoe and other top postal officials, while deriding the prepayment, say that the agency needs to make other changes, even after the agency consolidated mail processing centers and reduced hours at rural post offices.

Those changes include ending Saturday letter delivery, while still delivering packages, a growing part of the agency’s business, six days a week. The USPS has also reached an agreement to deliver packages from the online giant Amazon on Sundays in some locations.

With all that in mind, one postal observer off Capitol Hill said the Senate bill still has a ways to go before making it through the Homeland Security panel.

“There remains deep concerns about Saturday, rates and governance, service standards and more,” the observer said. “It may be time to consider a more streamlined approach to the bill.”

In fact, lawmakers have struggled to get postal reform legislation across the finish line for going on three years. The House Oversight Committee passed a measure in July, but the bill has yet to be scheduled for floor time.

The committee passed a measure in the last Congress as well, only to see GOP leaders keep it off the chamber floor, worried about what would have been a tough political vote,

The Postal Regulatory Commission is also expected to rule soon on a proposed postal rate increase opposed by sectors that use the mail, a decision that could also alter the debate on Capitol Hill.