If we can build 700 miles of wall, under GW Bush,
No wall was built under GW Bush. Only vehicle barriers and pedestrian fencing.
After over three years---Department of Homeland Security officials told us they have finished 649 out of 652 miles of fencing (99.5 percent), which includes 299 miles of vehicle barriers and 350 miles of pedestrian fence.
DHS reports there are currently 36.3 miles of double-layered fencing, the kind with enough gap that you can drive a vehicle between the layers. But the majority of the fencing erected has been vehicle barriers, which are designed to stop vehicles rather than people, and single-layer pedestrian fencing. The design specifications vary depending on geography and climate characteristics, but according to the Customs and Border Patrol website, it includes "post on rail" steel set in concrete; steel picket-style fence set in concrete; vehicle bollards similar to those found around federal buildings; "Normandy" vehicle fence consisting of steel beams; and concrete jersey walls with steel mesh.
That's not enough for some opponent of illegal immigration. "They are interpreting the requirements of the Secure Fence Act in a way that is clearly contrary to what Congress intended," said Mark Krikorian, executive director of the Center for Immigration Studies, which favors tougher enforcement against illegal immigration.
There may be a role for the vehicle barriers, but "your grandmother could hop over them," he said, and "that's not what Congress thought it was voting for."
https://en.wikipedia.org/wiki/Secure_Fence_Act_of_2006