Representative Will Hurd, Republican of Texas and one of the party’s most outspoken critics of the effort, called it the most expensive and least effective way to secure the border.

“We should be using the money we spend on border walls to invest in technologies such as sensors, camera, and other things, which are a fraction of the cost,” Mr. Hurd said.

But groups like the Center for Immigration Studies, which supports stricter limits on immigration, see the wall as a key element in the government’s efforts to secure the border and said it would most likely stem the flow of illegal drugs.

That position echoes statements by Mr. Trump, who has also said the wall would stop illegal immigrants and criminal organizations like the MS-13 gang.

But homeland security and migration experts say that a border wall is unlikely to stop either. They say the support for a wall ignores the changing dynamics of illegal immigration and the advances in technologies used by the Border Patrol and immigration officials.

“We have a much better picture of what’s happening on the border now more than we ever have,” said Doris Meissner, the top immigration official in the Clinton administration and a senior fellow at the Migration Policy Institute in Washington. “While a wall or barrier in some areas would be useful, trying to build one along the entire border would be wasteful because of all the technology we have and how illegal migration has changed.”