Twelve billion here, fifteen billion there, and pretty soon you’re talking about real money. Put them together, though, and it comes close to the actual projected cost of the border wall. Reuters reports that the Department of Homeland Security’s proposal runs far ahead of the funds that Republicans in Congress planned to allocate:

President Donald Trump’s “wall” along the U.S.-Mexico border would be a series of fences and walls that would cost as much as $21.6 billion, and take more than three years to construct, based on a U.S. Department of Homeland Security internal report seen by Reuters on Thursday.

The report’s estimated price-tag is much higher than a $12-billion figure cited by Trump in his campaign and estimates as high as $15 billion from Republican House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell.

The report is expected to be presented to Department of Homeland Security (DHS) Secretary John Kelly in coming days, although the administration will not necessarily take actions it recommends.

The plan lays out what it would take to seal the border in three phases of construction of fences and walls covering just over 1,250 miles (2,000 km) by the end of 2020.

It’s not the only variance from first projections. The new DHS study projects that the wall will be completed by late 2020, assuming Congress begins allocating the funds by May, presumably in the upcoming omnibus bill. That’s longer than the two-year estimate Kelly gave Congress just a week ago, which will certainly raise questions about his preparation for that testimony.

It also makes the issue of funding a little more fraught. Initially, Ryan indicated that the House would pursue the funding in the fall, as part of the FY2018 budget process. A two-year completion schedule at that point would have meant that the wall could be completed by late 2019, enough ahead of the presidential primaries to claim victory on a long-made promise from Republicans. A three-year-plus schedule suggests that the wall may not be complete until midway through an election year — and that gives Democrats plenty of reason to start blocking the funding, starting in two months during the omnibus FY2017 negotiations.

The time difference matters a lot more than the cash difference, though the latter is not exactly a few coins in the cushion. A nine-billion-dollar miss might seem like the lunch budget for the federal government, but it would actually be about 0.1% of all discretionary spending projected for FY2017 (although the appropriation will probably stretch out over the three-year period, too). At DHS, it’s more significant; the proposed FY2017 appropriation was $48 billion, so a $9 billion miss is rather big. Republicans might feel pressure from their conservative ranks to find the money by cutting other spending, and that will no doubt fuel opposition from Democrats.

It’s still probably better to have this fight earlier rather than later. If Ryan and McConnell wait until fall, the momentum for the project could stall, and Trump’s electoral mandate might have dissipated. Kelly better deliver it on time, and on budget, if Republicans want to reap political benefit from it. Besides, if they wait any longer, the bill’s just going to keep getting bigger and bigger.