Despite repeatedly claiming that Mexico would pay for the border wall, Trump requested and redirected billions of dollars for funding.

Trump repeatedly ran into funding difficulties through the official budget. The federal government shut down for 35 days starting in December 2018 when Trump refused to sign any funding bill that didn’t include money for the wall.

In March 2019, The Department of Defense is shifting $1 billion from a military personnel account to build a 57-mile fence

In August 2019, a quarter billion dollars were taken from FEMA, the federal organization responsible for disaster response and funding.

In September 2019, The Pentagon announced that 127 military projects would be delayed or suspended in order to provide $3.6 billion in funding for the wall.

In April, 2020, an additional half billion was pulled from overseas military construction projects.

In June 2020, the 9th Circuit Court of Appeals ruled that $2.5 billion in Defense Department funds were diverted illegally for the wall, as it was without congressional approval.

A private organization that sought to gain additional funding, We Build the Wall, raised approximately $25 million for the effort. In August 2020, longtime Trump ally and chair of the organization Steve Bannon was arrested for fraud and conspiracy to commit money laundering.

As of January 2020, from official and redirected funds, $11 billion had been spent on the wall at a cost of approximately $20 million per mile.

NPR – Pentagon Takes $1 Billion From Military Personnel Account To Build Border Fence
US News & World Report – Trump Administration to Redirect FEMA Money to Border
Vanity Fair – Trump Is Using More Pentagon Money to Pay For His Border Wall
Politico – Pentagon pulls money from overseas projects to pay for border wall
Wikipedia – We Build The Wall
NPR – $11 Billion And Counting: Trump’s Border Wall Would Be The World’s Most Costly