The Senate plans to vote in favor of a resolution that would block President Donald Trump’s recently declared national emergency later this week. Because the House already passed this resolution two weeks ago, its passage in the Senate will mean it has the approval of both chambers of Congress.

Trump is expected to veto the resolution, but legal experts tell Vox its passage would nonetheless send a strong message to the courts, indicating just how much Congress disagrees with him on the subject.

While the lawsuits that have been filed to challenge the emergency will be evaluated on a number of fronts, a clear objection to the emergency from Congress bolsters the case that Trump is bypassing Congress’s constitutionally granted “power of the purse” in order to obtain the funds he’s authorizing.

By voting to terminate the resolution, Congress is emphasizing that it doesn’t approve of using other designated funds to pay for the southern border wall. The legislative body’s actions might not have immediate teeth, but they could be used to argue that Trump’s efforts are, in fact, unconstitutional.

This congressional action comes as 16 states, including California, New York, and Michigan, have filed a legal challenge to the president’s decision to declare a national emergency to obtain funding for the wall.

“The challengers are arguing that the president is using emergency powers unconstitutionally to access funds Congress has been unwilling to appropriate,” says Liza Goitein, a co-director of the Liberty and National Security Program at the Brennan Center for Justice, who authored an expansive explainer on emergency powers for the Atlantic.

“With a majority of Congress voting for the resolution ... the argument that Congress has affirmatively approved the use of emergency military construction funds would be off the table,” Goitein adds. “A vote in favor of the resolution would thus preserve the record of Congress voting against funding for the wall, leaving the challengers’ constitutional argument intact.”

Congressional efforts to block the emergency could also undercut the president’s claim that there is a national emergency in the first place. The National Emergencies Act of 1976 gives presidents wide latitude to declare and define an emergency, but the pushback from Congress implies legislators don’t share Trump’s view that the wall warrants an emergency.

“When this issue gets to the courts, Congress’s view that no emergency exists might well affect how aggressively the courts review the president’s arguments to the contrary,” says Richard Pildes, a constitutional law professor at NYU.

There are a couple of legal issues courts will evaluate

Congress’s stance on the emergency will likely just be one issue that judges will evaluate as they weigh the many lawsuits that have been brought against the declaration. There are a couple of factors the courts will examine, says Michael McConnell, the director of Stanford’s Constitutional Law Center.

“The legal issues will be 1) standing; 2) whether the declaration of an emergency is judicially reviewable, and if so, whether this declaration was within the terms of the statute; and 3) whether construction of the wall is a ‘military’ project in service of the armed forces rather than in support of the civil law enforcement responsibility of DHS,” he tells Vox.

Here’s a look at how plaintiffs will have to address each of these questions:

1) Do plaintiffs have standing? In order to obtain “standing” in a challenge of the national emergency, plaintiffs will have to prove that they are being harmed by it in some way. This is the first obstacle they would have to overcome in order to levy their cases at all.

In the case of the states’ lawsuit against the Trump administration, the states are arguing that they are being harmed because the emergency could divert funding from state-based projects to construction of the wall. “We’re suing President Trump to stop him from unilaterally robbing taxpayer funds lawfully set aside by Congress for the people of our states,” California Attorney General Xavier Becerra said in a statement.

Others who could have standing to sue include landowners along the border whose property could be seized for wall construction. They could argue that such seizures would directly hurt them.

If they choose to pursue this route, congressional Democrats could also potentially have standing to sue. A 2014 case in which House Republicans sued the Obama administration over payouts to insurers under the Affordable Care Act could serve as precedent.

In that case, a federal judge granted standing to House Republicans, because they argued that the Obama administration was using funds to pay insurer subsidies that were not approved by Congress. This time around, Democrats could argue that the Trump administration is using funds that were not authorized by Congress for its wall.

2) Is the emergency judicially reviewable? Was it lawful? Because of how broad the National Emergencies Act is, it’s possible a court could determine that Trump simply has the ability to do what he wants under this statute.

As Sen. Rand Paul (R-KY) laid out in an op-ed outlining his position on the declaration, courts will have to decide if the emergency qualifies under the statute and, potentially, if it’s constitutional:

First, does statutory law allow for the president’s emergency orders, and, second, does the Constitution permit these emergency orders? As far as the statute goes, the answer is maybe — although no president has previously used emergency powers to spend money denied by Congress, and it was clearly not intended to do that. But there is a much larger question: the question of whether or not this power and therefore this action are constitutional.

In order to determine whether the National Emergencies Act can be used in the capacity that Trump has announced, courts will have to weigh whether the need for a border wall constitutes a national emergency. Again, presidents have historically had expansive discretion on this front, so Trump may have significant leeway, Stanford’s McConnell says.

However, comments that Trump himself made during his announcement about the emergency declaration could actually be used against him. “I could do the wall over a longer period of time, I didn’t need to do this, but I’d rather do it much faster,” he said in February, suggesting that the situation may not be so much of an emergency after all.

Becerra’s office has also argued that the “emergency” at the border that Trump keeps hammering is effectively rebutted by recent data, which shows that “unlawful southern border entries are at their lowest point in 20 years, immigrants are less likely than native-born citizens to commit crimes, and illegal drugs are more likely to come through official ports of entry.”

This is a part of the case where Congress’s likely decision to block the emergency could also come into play. With Congress shooting down the emergency, it could be tougher for the Trump administration to make the case that there is one.

On the question of constitutionality — if courts see this as a valid argument to review — Congress’s decision to terminate the emergency could help bolster the case that the declaration and its authorization of funds is, in fact, unconstitutional, since it’s actively going against Congress’s position on the subject.

3) Is construction of the wall a “military” project? There are many statutes a president can invoke when declaring a national emergency, and under the one that Trump is using, he will have to prove that construction of the wall qualifies as a “military” project.

Because border enforcement is typically seen as a civilian endeavor, this argument could be a tough one to make, former federal prosecutor Renato Mariotti tells Vox’s Sean Illing.

“Our border defense is primarily a civilian, not a military, operation,” he says.

Due to this distinction, it’s possible that courts could find that funding for the wall does not qualify under the statute that the Trump administration has identified, and decide he does not have the authority to repurpose these funds.

The Senate is expected to vote Thursday on the resolution to terminate the emergency. It’s a move set to have far-reaching political and legal implications.