The 5-4 ruling, which broke along ideological lines, means President Trump can tap into military funds to begin work to replace fencing along the southern border in California, Arizona and New Mexico. Earlier this month, the 9th U.S. Circuit Court of Appeals in San Francisco had agreed with a lower-court ruling that prevented the government from tapping that funding.
Trump declared a national emergency along the border to get up to $8.1 billion for wall construction, including the $2.5 billion from the Defense Department. He called the ruling a big win for "Border Security and the Rule of Law."
"Wow! Big VICTORY on the Wall. The United States Supreme Court overturns lower court injunction, allows Southern Border Wall to proceed. Big WIN for Border Security and the Rule of Law!" he tweeted.
Prominent Democrats criticized the court's logic and Trump's plans to use earmarked funds in an effort to come through on his signature campaign issue. Many argue a wall will not slow the flow of migrants into the United States.
Arizona Rep. Raul M. Grijalva, whose district runs along the U.S.-Mexico border, called Trump's emergency declaration a "pathetic attempt to circumvent Congress."
"Trump’s fake emergency was nothing more than a pathetic ploy to circumvent Congress and build his monument to his racist policies. This fight is not over, and I will continue fighting Trump’s efforts to destroy our environment and militarize border communities. #NoBorderWall," the Democrat tweeted soon after the ruling broke.
House Speaker Nancy Pelosi, D-Calif., called the ruling "deeply flawed" over Twitter.
"This evening’s Supreme Court ruling allowing @realDonaldTrump to steal military funds to spend on a wasteful, ineffective border wall rejected by Congress is deeply flawed. Our Founders designed a democracy governed by the people — not a monarchy."
For his part, Senate Minority Leader Chuck Schumer reminded his Twitter followers that when Trump was still a candidate for president, he promised that Mexico would pay for a border wall.
"It’s a sad day when the president is cheering a decision that may allow him to steal funds from our military to pay for an ineffective and expensive wall for which he promised Mexico would foot the bill," he posted.
He followed up with another tweet saying he hopes the courts will conclude Trump doesn't have the authority to build the wall.
Several Democratic presidential candidates also chimed in.
"Taking away money from the Defense Department to build a wall will not make us any safer. Trump’s political stunt will harm border communities & ignores the root causes of migration. We deserve a president with a common sense & compassionate immigration plan," former Housing Secretary Julian Castro tweeted.
Former Texas congressman Beto O'Rourke, also in the running for the Democratic presidential nomination, likewise expressed disappointment.
"Deeply disappointed in the Supreme Court’s decision. I’ve long opposed building walls, and while in Congress, I introduced language to prevent DOD funds from being used to plan or build a wall along our border. As President, I would do everything in my power to make that law."
"Congress did not appropriate these funds for Trump's medieval vanity project. Let's be clear: Trump's wall has never been about keeping the American people safe," tweeted California Sen. Kamala Harris.
"Diverting military funds for a vanity project is exactly who Donald Trump is. I will continue to fight back and join with those already challenging this wrong and misguided decision," New Jersey Sen. Cory Booker.
The American Civil Liberties Union said it plans to fight to keep Trump from using the funds for a wall that's already been denied by Congress.
Foe News reporter Alex Pappas contributed to this report.