SAN DIEGO -- One of President Trump's earliest campaign promises -- building a new and improved border wall to keep criminals and drugs out of the country -- is one step closer to fruition.

This week, the prototypes were finished in San Diego. U.S. Customs and Border Protection (CBP) will soon begin testing them, seeing how easy they are to climb over or dig under.

Four of the designs are solid concrete. The rest use steel and other materials.

The CBP is asking for a $1.6 billion down payment for 2018. Most of the money could go to begin building the wall, but it's a fraction of the overall estimated price tag of $21 billion.

In a report released earlier this year, the CBP's inspector general's office was skeptical that building a wall would make an impact.

"The southwest border is still porous and questions remain as to whether CBP's significant investments have resulted in better security," the report said. "We're not really dealing with immigration the way we should be."

"I think what the president is saying is, essentially trying to use this as a cover to pretend that he is responding to a promise that he made to his constituency," said Pedro Rios, director of the American Friends Services Committee.

Polls also show only 32 percent of Americans support the wall. Forty-nine percent oppose it, including 41 percent who are strongly against it.

But the CBP's acting deputy commissioner, Ronald Vitiello, says the need is evident.

"Border walls have proven to be an extremely effective part of our multi-pronged security strategy to prevent the illegal migration of people and drugs," Vitiello said.

However, Vitiello said completing the border wall is not guaranteed.

"There are a lot of things that have to make this work," he said. "I think the limiting factor is the appropriations for it."

Once the testing process is over, CBP will pick parts of each prototype that are most effective, but there probably won't be one singular winner. On top of that, the contractors that made the prototypes aren't guaranteed to make the final version of the wall. They'll have to go through another bidding process, but officials don't have a timeline for that process.