President Donald Trump is able to order the construction of a wall on the Mexico border with the stroke of a pen Wednesday, because of a 2006 law passed with the help of Democrats including Barack Obama, Joe Biden and Hillary Clinton.

The 2006 law authorized the construction of 700 miles of fencing along the southern border, as well as additional lights, cameras and sensors to enhance security. Although former President George W. Bush signed the measure into law, the Democrat-controlled Congress that took over a few months later ensured it would never be completed by means of an amendment to a 2008 spending bill.

The amendment removed an explicit requirement the wall be made of double-layer fencing, and gave the Department of Homeland Security authority to put in place less effective barriers, such as simple vehicle barriers that do not keep pedestrians out. As a result, Democrats were able to avoid a politically unpopular vote against the wall, and then turn around and quietly gut its construction. But Trump and Republicans in the new Congress now plan to use that law to ensure a proper wall is constructed.

Since the law was never actually repealed, the federal government is still authorized to build a substantial wall on the southern border. Congress doesn’t have to pass a new law to begin construction, and can instead package the funds necessary into a massive spending bill Democrats would have a politically hard time opposing. Trump may get a head start on the process by diverting other funds congressional leaders have indicated are available for the project, ensuring a snafu over the spending bill doesn’t hinder prompt construction of the wall.

If Trump and Republicans follow through, a number of top Democrats will find they inadvertently handed Trump the border wall they now oppose. Their only option to block the construction would be to shut down the government over the matter by blocking the spending bill, a strategy they have consistently mocked and derided Republicans for using in the past.

In addition to then Sens. Obama, Biden and Clinton, 64 House Democrats and 23 Senate Democrats voted for the wall in 2006. Many of them are still in Congress, including newly-established Senate Minority Leader Chuck Schumer.

Other Democrats in the Senate who voted for the wall in 2006 are Sens. Barbara Boxer (Calif.), Sherrod Brown (Ohio — then in the House), Tom Carper (Del.), Dianne Feinstein (Calif.), Barbara Mikulski (Md.), Bill Nelson (Fla.), Debbie Stabenow (Mich.), and Ron Wyden (Ore.).

There are also a number of Democratic representatives still in the House who voted for the bill: Sanford Bishop (Ga.), Corrine Brown (Fla.), Michael Capuano (Mass.), Jim Cooper (Tenn.), Jim Costa (Calif.), Peter DeFazio (Ore.), Steve Israel (N.Y.), Ron Kind (Wis.), Daniel Lipinski (Ill.), Stephen Lynch (Mass.), Carolyn Maloney (N.Y.), Bill Pascrell Jr. (N.J.), Collin Peterson (Minn.), C.A. Dutch Ruppersberger (Md.), Tim Ryan (Ohio), and Adam Smith (Wash.).

Former Democratic Rep. Barney Frank and now-disgraced former Democratic Rep. Anthony Weiner also voted for the bill.

President-elect Donald Trump made the construction of a “real” wall along the entire 2,000-mile stretch of the southern border with Mexico a central part of his campaign. He has said the “beautiful” wall will be from 35 to 50 feet high and made of pre-cast concrete.

“I would build a great wall, and nobody builds walls better than me, believe me, and I’ll build them very inexpensively,” he said in his speech announcing his candidacy for the presidency. “I will build a great, great wall on our southern border. And I will have Mexico pay for that wall. Mark my words.”

(Editor’s note: This post was previously published January 6 under the headline “Democrats Handed Trump His Border Wall.” It has been updated to reflect new developments in the president’s plan to build the wall.)

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