While their goals like a higher minimum wage and “Medicare for All” have gained traction among Democrats, Senator Sanders and his allies have struggled to win elections.
With the president’s approval rating at 90 percent among Republicans, many supporters say they defend Mr. Trump even with some misgivings because they feel criticism of him is constantly overblown.
The president tweeted demands on Thursday — change the laws, build a wall, do not hire immigration judges — as his administration scrambled to execute his latest executive order.
In border states, Republican voters say that whatever sympathy they feel for children separated from parents is complicated by frustration over the flow of undocumented immigrants from Mexico.
It is unclear how Mr. Trump intends to claim the legal authority to violate what have been legal constraints on the proper treatment of children in government custody.
While Senate Republicans focus on narrow legislation intended to keep families together, Speaker Paul D. Ryan promoted a wide-ranging immigration bill that is up for a vote on Thursday.
The homeland security secretary has become a top advocate for President Trump’s family separation policy as illegal border crossings continue to surge.