The Senate will vote Thursday on a border security bill that is dividing the Democratic caucus and failed earlier this year, exposing rifts within the party even as they try to shift the narrative on border security.

As immigration remains top of mind for voters, the White House and top congressional Democrats have discussed a series of moves aimed at strengthening their hand on border security ahead of the first presidential debate next month. Sources say those talks included reviving the stalled border security measure that initially failed after former President Donald Trump told GOP lawmakers to knock it down.

Democrats have pointed to the failure of the bill – which was negotiated on a bipartisan basis – to argue that Republicans are not serious about trying to fix problems at the southern border and are ready to ramp up that argument after the bill stalls out a second time as expected.

But without Ukraine tied to the measure, some Democrats and immigrant advocates are casting it as purely political and taking issue with key elements of the bill – one of the toughest border measures in recent memory. It’s a dynamic that threatens to undermine the messaging effort from Democrats and the White House.

“I will not vote for the bill coming to the Senate floor this week because it includes several provisions that will violate Americans’ shared values. These provisions would not make us safe,” Sen. Cory Booker, a New Jersey Democrat, said in a statement Tuesday.

Booker voted to advance the bill in February when it failed 49-50. In his statement, Booker noted that the first time around the bill also included “critical foreign and humanitarian aid.”

Republicans have largely dismissed the vote as a political move for vulnerable Democrats to seek political cover over a major issue in the run-up to the November elections.

Senate Majority Leader Chuck Schumer acknowledged over the weekend that not every Democrat may vote for the bill in a letter to colleagues. Sixty votes are needed to break a GOP filibuster attempt. Democrats only have 51 votes total and most Republicans have already said they plan to vote against the effort.

The border bill was a topic of discussion Tuesday during Democrats’ closed door party lunch as members debated the merits of bringing up a bill that has already failed to advance in the Senate. A source in the room told CNN that the vast majority were supportive, but that there were holdouts.

Sen. Alex Padilla, who opposed the bill the first time around, said he will vote against the bill when it comes to the floor on Thursday.

“It’s also not lost on me that the last time we were here, a lot of people mentioned this was the price they were willing to pay for the sake of Ukraine funding. That is no longer the case,” Padilla said, acknowledging that something needs to be done to address the border. “This should not be the Democratic starting point for border security.”

Virginia Democratic Sen. Mark Warner said the fact there may be internal backlash incentivizes some moderates: “Frankly, the fact that some of our most progressive members don’t vote for it, in my mind, is an indication that it really was a true bipartisan, tough bill,” he said.

If passed, the bill would dramatically change immigration law for the first time in decades. It includes, for example, a new emergency authority to restrict border crossings if daily average migrant encounters reach a certain level, raises the legal standard of proof to pass the initial screening for asylum and expedites the asylum processing timeline, among other measures.

Most Republicans view the vote as largely a messaging exercise for Democrats. But Republican Sen. Lisa Murkowski of Alaska, who previously voted for the bill, indicated she could back the bill again, despite calling the process “dumb.”

“If I thought it was good enough to vote for before, what changed?” Murkowski said. “Explain what is going on to someone who is not in this building. They think we’re nuts.”

But Republican Sen. James Lankford, a key negotiator on the border bill, said he’ll vote against the measure Thursday. “It’s no longer a bill. It’s a prop,” he told CNN’s Kaitlan Collins Tuesday.

Democrats have sought to shift blame onto Republicans for not securing the border, citing their decision to walk away from a measure that restricted migrants’ ability to seek asylum at the US southern border, among other restrictions.

The message became a winning one in New York’s third congressional district in February when Democratic Rep. Tom Suozzi went on offense on immigration and won the seat.

The absence of foreign aid and inclusion of what some immigrant advocates describe as sharp policy has turned up the volume on criticism.

“It is unconscionable and deeply disappointing for Senator Murphy to be championing these policies that will simply not work, and for Leader Schumer, the senator from the home to the Statue of Liberty, to be pushing for this vote,” Robyn Barnard, senior director of refugee advocacy at Human Rights First, told CNN.

“The American public were told these harsh policies were necessary to secure Ukraine funding earlier in the year, what is their excuse for adopting anti-immigrant policies now?” Barnard said.

The pressure on Congress also reflects the limited tools the administration has at its disposal to affect the situation on the ground over the next few months.

“We recognize that there are limits to what any administration can do in this space with executive action,” one senior administration official said. “What we really need here and we continue to call for is for Congress to do its job and to take up and pass the Senate bipartisan border security legislation.”

Senior administration officials are bracing for the potential that border crossings will surge this summer, like in previous years and are trotting out a series of policy changes to try to dissuade migrants from journeying to the US – and convince skeptical voters they are working to tighten up immigration at the border.

“All of the factors that have been driving this unprecedented movement of people all over the world remain and we continue to be very vigilant and work, night and day to try to put policies in place that will mitigate its impact on our border,” this senior official said.

Discussions are ongoing on rolling out a border executive action, according to sources, who say that one of the considerations is doing so after Mexico’s election in early June and potentially before the first presidential debate.

It’s all part of a broader strategy to remind voters they have a plan, Democrats say.

“We’ve seen some pretty encouraging polling that indicates that once people know what we have the strongest, bipartisan border bill in generations and we are prepared to do real and tough things that moderates are willing to change their view about Democrats and border security,” said Sen. Brian Schatz, a Democrat from Hawaii.

“It’s a good bill and it is something that needs attending to. That’s our job. Let’s bring it up,” said Maine Sen. Angus King, an independent who caucuses with Democrats.