Homeland Security Secretary John Kelly acknowledged Wednesday that President Donald Trump’s proposed wall on the southern border of the United States will not extend “from sea to shining sea” and could partially be fencing.

Kelly had few details about the size and scope of the wall when he testified in front of the Senate Homeland Security and Governmental Affairs Committee, saying the administration would rely on the input of those working on the border for the specifics.

"There is no way I can give the committee an estimate of how much it will cost," Kelly said. "I don’t know what it will be made of, I don’t know how high it will be, I don’t know if it’s going to have solar panels on its side and what the one side is going to look like and how’s it’s going to be painted."

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"It’s unlikely that we will build a wall or physical barrier from sea to shining sea. But it is very likely, I’m committed, to putting it where the men and women say we should put it," he added.

A wall on the 2,000-mile border between the U.S.and Mexico was a signature campaign promise for Trump as part of his pledge to cut down on illegal immigration. He also declared that Mexico would pay for the barrier, despite consistent insistence by Mexican officials that they will never fund it.

The White House made a request for $1 billion to begin construction of the wall as part of its push to boost spending on defense and border security. But Democrats have vowed to block funding for the barrier and Republicans are wary of lumping the border request in with a broader spending bill to prevent a government shutdown before the April 28 deadline.

"The sooner we stop this, you know, we’re going to build a wall from sea to shining sea and the Mexicans are going to pay for it; it’s embarrassing," Democratic Sen. Claire McCaskill said Wednesday. "It’s not going to happen. Everybody in Congress knows it’s not going to happen."

The first round of bids for contractors hoping to construct the wall were due Tuesday. Senate Majority Leader Mitch McConnell estimated the full wall would cost between $12 to $15 billion, but a CNBC analysis found that number could rise up to $25 billion plus millions in annual maintenance.

In written testimony submitted to the committee, Kelly credited the president for a declining number of arrests of people caught trying to illegally cross the border. The head of Homeland Security said March was the fifth straight month border arrests declined and marked the lowest monthly number of arrests in the last 17 years.

"We’ve seen an absolutely amazing drop in the number of migrants coming out of Central America taking that terribly dangerous route from Central America into the United States," Kelly said. “It won’t last unless we do something, again, to secure the border. The wall, or physical barrier, something to secure our border.”

White House press secretary Sean Spicer said in a statement that the drop in arrests "demonstrates that the President's commitment to securing our border and supporting law enforcement is already showing results."