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Department of Defense has redirected $1 billion in funding for the wall Image Credit: Creative Commons

Update: An effort by House Democrats to override President Donald Trump's first veto has failed. That hands him a victory because his declaration of a national emergency at the Southwest border will remain in effect.

The Democratic-controlled chamber has voted 248-181 in favour of overriding Trump's veto. That fell 38 votes short of the 286 needed for Democrats and their handful of Republican allies to prevail, because a two-thirds majority was needed.

The emergency declaration would let Trump shift an additional $3.6 billion from military construction projects to erecting barriers along the border with Mexico. Building the wall was one of Trump's most repeated campaign pledges, though he said it would be paid for by Mexico, not taxpayers.

Congress voted to provide less than $1.4 billion for barrier construction. Court challenges may eventually block the extra money Trump wants.

The Department of Defense has redirected $1 billion (Dh3.67 billion) in funding to allow construction of some of Donald Trump's border wall, it announced late on Monday night, in a move Democrats said would worsen existing "substantial shortfalls" in defense spending.

Patrick Shanahan, the acting defense secretary, said the $1 billion would go towards 57 miles of 18 foot-high fencing and other measures along the border, CNN reported .

The construction would represent the first new section of Trump's long-promised border wall, and gives yet another political boost for the president after the special counsel Robert Mueller found no evidence of collusion between the Trump campaign and Russia.

In a letter to homeland security secretary, Kirstjen Nielsen, Shanahan said he had authorised the Army Corps of Engineers to commence planning and construction of the wall near the Yuma and El Paso sections of the border, according to CNN.

The move comes after Trump issued a much-disputed national emergency declaration for the border in February, following a five-week government shutdown initiated by the president in an attempt to secure funding for the wall. In February Republicans joined with Democrats in the House and Senate to pass a resolution which would have ended the national emergency, but the president vetoed the measure.

The House is planning a vote on Tuesday to override Trump's veto, but is expected to fall short of the two-thirds majority required.

In a letter to Shanahan a group of Democratic senators who sit on subcommittees on defense and military construction, veterans affairs and related agencies accused the Department of Homeland Security of allowing "political interference and pet projects to come ahead of many near-term, critical readiness issues facing our military".

"We strongly object to both the substance of the funding transfer, and to the Department implementing the transfer without seeking the approval of the congressional defense committees and in violation of provisions in the defense appropriation itself," the senators, including Tammy Baldwin, Dianne Feinstein and Richard Durbin wrote.

"The $1 billion reprogramming that the department is implementing without congressional approval constitutes a dollar-for-dollar theft from other readiness needs of our Armed Forces."