Washington (CNN) Vice President Mike Pence is meeting privately with five Republican senators on Tuesday as the White House continues to ramp up pressure on lawmakers rebuking President Donald Trump over his national emergency declaration on the southern border.

The vice president is expected to sit down with Sens. Thom Tillis, Mike Lee, Rob Portman, Pat Toomey and Lamar Alexander, according to an administration official, as the West Wing is becoming increasingly concerned that the vote will turn into an embarrassing rebuke for Trump.

So far, four Republicans -- Sens. Susan Collins, Lisa Murkowski, Rand Paul and Tillis -- have said they will support the resolution, which amounts to a presidential admonishment. CNN reported last week that the White House has been pressuring Republicans to vote against the resolution, warning those who don't get in line that there could be 2020 election consequences.

Administration officials believe that if only a handful of Republicans support the resolution, it won't be as significant of a problem because some opposition is expected. But if that number grows to 10 Republican senators or more, those officials worry about the optics of the intra-party split.

Speaking Tuesday at the Credit Union National Association's Governmental Affairs Conference, Pence said a vote against the President's emergency declaration is a vote against border security. He called on senators to stand up for border security and stand with Trump.

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