President Trump is attempting to use a national emergency declaration to secure more funding for border barriers than Congress has authorized. (Jorge Silva/Reuters)

The White House sought to ratchet up public pressure Wednesday on Republicans considering bucking President Trump on his national emergency declaration, dismissing concerns some have voiced about setting an unwise precedent and urging them to stay united.

A pointed tweet from Trump and a public warning from a senior aide came as the administration scrambled to limit GOP defections ahead of a vote next week to nullify Trump’s emergency declaration on the U.S.-Mexico border.

Trump is attempting to use the declaration to secure more funding for border barriers than Congress has authorized — a move that Democrats and some Republicans have cast as an encroachment on their constitutional powers.

“Senate Republicans are not voting on constitutionality or precedent, they are voting on desperately needed Border Security & the Wall,” Trump said in an early afternoon tweet. “Our Country is being invaded with Drugs, Human Traffickers, & Criminals of all shapes and sizes. That’s what this vote is all about. STAY UNITED!”

Senate Majority Leader Mitch McConnell (R-Ky.) has acknowledged that the measure rebuking Trump is likely to pass, but it does not appear to have enough widespread support to survive a threatened presidential veto.

Some of the GOP senators who have said they will support the resolution to nullify the emergency declaration — including Susan Collins (Maine) and Thom Tillis (N.C.) — have made their case for the separation of powers and the need to protect congressional prerogative, particularly on deciding how taxpayer money is spent.

Two other Republicans, Sens. Lisa Murkowski (Alaska) and Rand Paul (Ky.), have said they will join Democrats in voting for the resolution, with Paul predicting that more GOP senators will join them.

Several wavering Republicans have voiced concerns about Trump setting a precedent for future Democratic presidents to take similar actions on other policy issues on which they don’t get their way with Congress.

Asked Wednesday morning whether she has a message for Republicans considering voting against the president, White House press secretary Sarah Sanders responded sharply.

“My message to that group is to do your job,” she said during an appearance on Fox News’s “Fox & Friends.” “If you had done what you were elected to do on the front end, the president wouldn’t have to fix this problem on his own through a national emergency.”

During the Fox interview, Sanders also pointed to a surge in migrants being detained at the border as further justification for Trump’s emergency declaration.

Last month was the busiest February at the border since 2007, with authorities detaining 76,103 migrants, up from 58,207 in January, according to U.S. Customs and Border Protection figures released Tuesday.

“If that doesn’t define crisis, I don’t know what does,” Sanders said.

“Congress should have fixed this problem,” she added. “The president tried multiple times to get Congress to work with him to address the crisis. They failed to do so, and now the president has to do what is absolutely necessary and what is right, and that is to declare a national emergency and fix the crisis at the border.”

Trump declared the emergency on Feb. 15 to try to tap $3.6 billion allocated for military construction projects. The administration is also accessing $601 million from a forfeiture fund in the Treasury Department and $2.5 billion from a Pentagon counterdrug account, which it can do without an emergency declaration.

During her television appearance, Sanders also criticized House Democrats for a sweeping investigation launched this week into whether Trump and his administration have been involved in corruption and abuse of power.

“It is an absolute embarrassment that members of Congress are using all of their time and resources into attacking the president when they should be looking at trying to solve problems that this country has, like the president is doing,” Sanders said. “They should follow his example of coming to work every day and looking at how they can help the American people, not how they can attack this president.”

Seung Min Kim, Erica Werner and Nick Miroff contributed to this report.