Donald Trump’s proposed multi-billion dollar border wall is running into some roadblocks of opposition among Senate Republicans, according to CNN’s Manu Raju. He reports that many Republicans “bluntly told CNN they'd likely vote against any Trump plan that is not fully offset with spending cuts” while also noting some gentle substantive objections from some members of the caucus.

The most noteworthy of the objectors is Senator John Cornyn of Texas, both because he is the number two Republican in the Senate, and also because he’s from Texas — right on the border.

"I don't think we're just going to be able to solve border security with a physical barrier,” he told Raju, “because people can come under, around it and through it."

This is in stark contrast to the posture of House Speaker Paul Ryan, who is both eager to appropriate billions of dollars for the wall, and to go along with the fiction that congressional appropriations would just be an advance on hypothetical repayment. As recently as October, Ryan was saying he would “no longer defend” Donald Trump on the grounds that he’d been caught on tape confessing to a casual acquaintance that he routinely sexually assaults women. But that was when Ryan thought Trump was going to lose. Since he won, Ryan’s strategy for gaining Trump’s support for his own passion project of taking assistance away from poor people has been to support whatever Trump says or does.

The Senate seems less inclined to about-face.

Texas doesn’t want the wall

A key issue here is that Texas is a large conservative state that sends many influential Republicans to congress. It’s on the US-Mexico border, and while much of that border already features walls or fences, much of the Texas border does not. This is, in part, because Texas does not want this wall. The closer you get to where it would be built, the less people want it.

Will Hurd (R-TX) who represents far-and-away the largest swathe of currently unwalled border — from the outskirts of El Paso down almost to the other end of the stat has been particularly vocal about this, calling it “unnecessary” and “too expensive.” He has separately referred to it as “wasting hard-earned taxpayer dollars.”

A big part of the issue is that unlike in Arizona and New Mexico where the border runs along a very straight line largely through federally owned land, in Texas the border follows a squiggly natural boundary and goes through privately owned land.

Trying to literally conform a border wall to this fractal terrain would be ridiculous. Any feasible construction project is going to need to be straighter than the actual border, which is going to mean using the federal government’s eminent domain powers to take privately owned land and basically redraw the border. This has been a flashpoint between Trump and elements of the ideological right in the past, since he’s an enthusiastic proponent of using eminent domain to benefit private economic development projects, which many conservatives regard as unconstitutional.

A border wall — unlike a parking garage for an Atlantic City casino — is pretty clearly meant to serve a public function, so the constitutional issue wouldn’t necessarily arise. Nonetheless, it’s generally the case that people don’t like it when the government comes in and takes their land. And it’s easy to imagine they particularly wouldn’t like it if the government came in to take their land so that the president of the United States could avoid admitting that one of his campaign promises was kind of dumb. Moreover, it’s questionable it even would serve its stated purpose . Unauthorized immigration from Mexico has already slowed to a trickle (indeed, by most estimates more people are leaving than arriving), and the un-walled area in particular has almost no border crossings since it’s in the middle of nowhere.

It’s worth noting that the sections of Texas where fences have been built in the past report that it’s inflicted hardship on the area, and when the Texas Tribune surveyed the state’s 38-member congressional delegation it found that none of them wholeheartedly supported the border wall scheme.

Fiscal issues could doom the wall

Beyond the specific local objections to the wall, the fiscal cost looms large.

The $12-$15 billion that it would cost isn’t beyond the fiscal capacity of the United States, but it is a lot of money to spend on what amounts to a pet project for the president. Insisting on offsetting it with spending cuts is a pretty unassailably conservative position — conservatives are supposed to be against spending, after all — that should protect anyone who wants to do it from their base.

Meanwhile, the White House is poorly positioned to argue that the wall needs to be deficit-financed because the president rather famously promised that Mexico — rather than America’s children — will pay for the wall. By the same token, putting together a package of offsetting spending cuts will be very difficult to sell because, again, Trump promised that Mexico will pay for the wall.

Meanwhile, it’s unlikely red-state Democrats feel particularly pressured to bail Trump out on this, because they can always say that they want what their constituents voted for: Trump’s promise that Mexico will pay for the wall.

Which means that in fiscal terms all roads more or less lead back to Trump’s campaign pledge, which was to make Mexico pay for a border wall. The Trump White House, of course, has no way of making this happen since Trump has rendered himself so politically toxic in Mexico that it would be suicide for any Mexican politician to agree to any deal that could even possibly be construed as Mexico paying for a border wall. This has left the administration flailing, suggesting at one point that broad corporate income tax reform might somehow constitute Mexico paying for the wall.

All of this could be moot, however, since it’s rarely been clear how serious Trump himself is about the wall. Newt Gingrich opined shortly after the election that it was a mere “campaign device.” A lot of the border is already walled or fenced, and Homeland Security Secretary John Kelly just suggested that a “see-through” wall composed of sensors could do the job.

Which leaves open one possibility: it wouldn’t be very difficult to appropriate some money for some additional wall construction. That would be enough for Trump to make a visit to a border wall construction site and declare victory — while Republican senators relieved to have avoided paying $14 billion for a wall would surely be happy to let Trump have the political win.