Acting Customs and Border Protection Chief Mark Morgan expressed uncertainty in regards to whether or not the Trump administration will be able to achieve its goal to build a wall along the southern border by the end of President Trump’s first term in office.

Trump’s demand for a wall separating the United States and Mexico was one of his earliest campaign promises, and yet as of last month, the administration has yet to build any part of the wall where there wasn’t fencing previously located. The president, while it’s unclear as to the final path for the wall, has promised to build 450 miles of it along the border by 2021.