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Donald Trump’s dispatch of military troops to the US border with Mexico is currently on track to cost American taxpayers over $600 million, Pentagon officials said Jan. 29, and that number is likely to climb much higher.

The Trump White House ordered the military to send over 5,000 active duty military to the southern US border last October, just before the midterm election, as a caravan of asylum-seekers wound its way on foot through Mexico. “Operation Faithful Patriot” joined thousands of National Guard troops who had been at the border since April of 2018, despite a historically low number of apprehensions of border-crossers.

So far, active duty troops on the border have cost taxpayers $132 million, Pentagon officials testified to Congress today. The National Guard troops have cost $103 million; they are expected to stay at the border through the 2019 fiscal year that ends in September for an additional cost of $448 million, they said.

These numbers could rise significantly. Acting Defense Department Secretary Patrick Shanahan told reporters today “several thousand” more troops were being dispatched to the southern border “soon,” following a DHS request, at a likely cost of tens of millions more.

By dispatching troops to the US southern border, Trump followed in the footsteps of predecessors Barack Obama and George W. Bush, who both spent millions of dollars dispatching troops there with little to show for it:

In 2006, Bush’s “Operation Jump Start” sent 6,000 National Guard troops to the US-Mexico border, where they did everything from help seize drugs to rescue a drowning Central American woman. It cost $1.2 billion over two years.

Obama’s 2010 “Operation Phalanx” sent 1,200 National Guard troops to the border for 14 months, for a total cost of $145 million.

Both the Bush and Obama operations took resources from other Department of Defense projects, while failing to establish a transparent US-Mexico border security policy, the Government Accountability Office said in a critical 35-page report.

Trump held dozens of rallies around the US falsely claiming that immigrants from Mexico and Central America were a serious security threat, in an attempt to get his base to vote for Republicans in the midterm elections. The strategy backfired.