Gen. John Kelly sailed through his Senate confirmation to head the Department of Homeland Security. President Trump’s next nominee isn’t likely to be so lucky.

Democrats raised few objections when Trump picked Kelly to head DHS at the beginning of his presidency, viewing him as the best they could hope to oversee the implementation of Trump’s controversial plans on undocumented immigrants and refugees and deciding to use their efforts to battle other more vulnerable cabinet picks.

Many knew Kelly from his time as a high-ranking marine, and hoped he would stand up to Trump on some of his most draconian and unrealistic demands. He cruised through his committee hearing and was confirmed by the full Senate on an 88-11 vote as Senate Democratic leaders left him off their list of Trump nominees to target for defeat.

Since then, however, Democrats have been sorely disappointed that Kelly hasn’t done more to fight Trump’s worse impulses or rein in his ICE agents as they dramatically ramped up deportations and split up families. With his exit to become Trump’s chief of staff, there are signs that whoever the president names is in for a battle.

The Senate Homeland Security Committee isn’t exactly set up to be a home for the anti-Trump resistance — four of the committee’s seven Democrats hail from states Trump won, and three of them face reelection next year. But some of those Democrats indicate they’re ready to show more backbone this time around.

“There’s going to be an opportunity to recap what they’ve done and why they’ve done it and see if we can make it so that families aren’t torn apart,” Sen. Jon Tester (D-MT), who backed Kelly’s nomination in the committee and the full Senate, told TPM Monday evening. “It gives us an opportunity to make the process work better. We’ll see in the end, but it gives an opportunity to ask some important questions.”

While there have been reports that Kelly has stood up to the president on certain issues including the Muslim ban, many Democrats have been dismayed by his company man attitude and his fierce defense of ICE agents as they executed wholesale roundups of undocumented immigrants, split up families and dismissed normal protocols for prioritizing the deportation of violent criminals ahead of otherwise law-abiding border-crossers. Kelly fired back hard at any criticism of his agents or his department, telling lawmakers in public and private that if they didn’t like how his agents were doing their jobs they should change the law.

“A number of my colleagues have said to me they regretted their vote for him,” Sen. Richard Blumenthal (D-CT), one of the 11 Democrats who voted against Kelly, told TPM.

The big question is who Trump will nominate. Rumors have flown that Attorney General Jeff Sessions could be moved over to the department.

“We’ll see what happens with the attorney general, that’s certainly a matter of major interest right now. There’s been talk about him taking Homeland Security. That would be extremely contentious,” Sen. Ben Cardin (D-MD) said.

But that seems unlikely since Trump has even less trust in Sessions’ deputy than his former close ally turned punching bag, and the move would set up a huge fight over Sessions’ replacement, as well as an eventual battle to confirm Sessions himself (that would be delayed since Sessions has already been confirmed by the Senate fir his current post).

Democrats also say they know little about Elaine Duke, Kelly’s former deputy and now the acting head of the agency. Duke could be the pick, sidestepping a bigger confirmation fight since she’s already in charge. House Homeland Security Chairman Michael McCaul (R-TX), a Trump loyalist but one that is respected across the aisle, could also face less of a fight.

But controversial Kansas Secretary of State Kris Kobach has long pined for the position and has been rumored to be in the mix as well. A Kobach nomination would likely spur a brutal confirmation fight focused on his long involvement in anti-immigration efforts (he wrote Arizona’s draconian immigration law and many other states’) as well as his crusade against voter fraud.

Democrats say that they’re bracing for a fight over the nomination, planning to use it to reevaluate how the department is being run and spotlight Trump’s anti-immigrant crusades, which many say have flown under the radar as other Trump scandals and the GOP’s Obamacare repeal fight have dominated the headlines.

“We should take a look at exactly what has happened as opposed to just the words people speak about their intentions. There was a lot of what happened in the confirmation hearings writ large that was about ‘who will speak truth to power’ and I think the time that has passed since that first wave of confirmations has given us the chance to really see whether people really speak truth to power and walk truth to power in terms of their actions,” said Sen. Kamala Harris (D-CA), the lone Democrat to vote against Kelly’s confirmation on the committee.

“The solution here is not rounding people up who are undocumented in this country and deporting them,” Sen. Catherine Cortez Masto (D-NV) said. “I’m looking for somebody who is fair and balanced … who understands that on the front lines the men and women in [ICE] have discretion and they need to be given guidance on how to use that discretion.”