Since ar­riv­ing in the Sen­ate six years ago, Rand Paul has been a con­sist­ent thorn in the side of Demo­crats and Re­pub­lic­ans alike on for­eign policy. And that’s not go­ing to change, even once a mem­ber of his own party oc­cu­pies the Oval Of­fice.

As Don­ald Trump has rolled out his Cab­in­et picks over the past few weeks, few mem­bers of Con­gress have been as out­spoken about them as Ken­tucky’s ju­ni­or sen­at­or, who had been lay­ing re­l­at­ively low after his exit from the pres­id­en­tial race in Feb­ru­ary. On the do­mest­ic front, Paul has been quite sup­port­ive, prais­ing Trump’s se­lec­tions to head the Health and Hu­man Ser­vices, Trans­port­a­tion, and Edu­ca­tion de­part­ments.

On for­eign af­fairs, though, Paul—who has long clashed with hawks in his own party—has been com­bat­ive, es­pe­cially as Trump has con­sidered po­ten­tial nom­in­ees for sec­ret­ary of State in a very pub­lic fash­ion. Paul has raised the pos­sib­il­ity of block­ing John Bolton and Rudy Gi­uliani, say­ing they are “un­re­pent­ant in their sup­port for the Ir­aq War.” He ques­tioned how Re­pub­lic­ans could con­firm Dav­id Pet­raeus, who was con­victed of mis­hand­ling clas­si­fied in­form­a­tion, “with a straight face.” And he’s in­dic­ated that he still wants to hear more from Mitt Rom­ney.

Giv­en his perch on the Sen­ate For­eign Re­la­tions Com­mit­tee—with its 10-9 par­tis­an roster—as well as the GOP’s slim ma­jor­ity in the up­per cham­ber, Paul is in a po­s­i­tion to cause some ser­i­ous head­aches for Trump not just dur­ing the Cab­in­et con­firm­a­tion pro­cess, but throughout the early stages of his White House ten­ure as his for­eign policy be­gins to take shape.

“Rand is not the kind of guy to be a stick in the mud on everything,” said one Re­pub­lic­an strategist fa­mil­i­ar with Paul’s think­ing. “But where he will put his foot down will be on the is­sue of for­eign policy, and that should not come as any sur­prise to any­body in the Trump or­bit.”

Paul has been open to one of Trump’s re­por­ted sec­ret­ary of State fi­nal­ists: Bob Cork­er, the chair­man of the For­eign Re­la­tions Com­mit­tee. Paul has pre­dicted the sen­at­or from Ten­ness­ee, who said he has not spoken with any of his col­leagues about the pos­sible move, would “sail through” with bi­par­tis­an sup­port.

Re­gard­less of who Trump ap­points to run the State De­part­ment, Paul’s col­leagues said they see him play­ing a sim­il­ar, vo­cal role on for­eign policy un­der Pres­id­ent Trump as un­der Pres­id­ent Obama.

“He’s been very act­ive and been a great con­trib­ut­or, and I would ima­gine he will con­tin­ue to be a strong voice in for­eign policy,” Cork­er said.

Demo­crats who share some of Paul’s non­in­ter­ven­tion­ist views think he will be­come an even more im­port­ant ally now that they are set to be­come the minor­ity party in Wash­ing­ton. Sen. Chris Murphy said he hopes that his fel­low For­eign Re­la­tions Com­mit­tee mem­ber will serve as a check on Trump’s al­lies who are more open to in­ter­ven­tion abroad. He ad­ded that he would work with Paul on a new au­thor­iz­a­tion for the use of mil­it­ary force, which Sen. Tim Kaine re­newed his call for on Wed­nes­day, to fight the Is­lam­ic State.

“I ex­pect that Rand is go­ing to con­tin­ue to be Rand. He’s got a very clear-eyed view of Amer­ica’s role in the world, one that I agree with more of­ten than I dis­agree with it,” Murphy said. “I think there’s go­ing to be a lot of hawks around Don­ald Trump, and Rand is go­ing to be an im­port­ant voice in that party.”

Of course, Paul will con­tin­ue to face res­ist­ance from the wing of the GOP that in­cludes na­tion­al se­cur­ity stal­warts John Mc­Cain and Lind­sey Gra­ham. Both sen­at­ors have ex­pressed sup­port for Pet­raeus to be­come the next sec­ret­ary of State.

“He’s free to do what he wants to do, but I can as­sure you that his views about John Bolton or Pet­raeus … are not shared by any­one but him,” Mc­Cain, the chair­man of the Sen­ate Armed Ser­vices Com­mit­tee, said of Paul. Asked if Paul’s role on for­eign policy will change dur­ing the new ad­min­is­tra­tion, Mc­Cain curtly re­spon­ded, “He has no fol­low­ing.”

Just how much com­mon ground Trump and Paul will find re­mains to be seen. Paul said he de­cided to en­dorse his former rival dur­ing the gen­er­al elec­tion in part be­cause Trump now views the Ir­aq War as a mis­take, even though he pre­vi­ously spoke in fa­vor of it. Once Trump is sworn in on Jan. 20, he will need to quickly be­gin filling in a lot of blanks on for­eign policy. Some ex­perts think that his total in­ex­per­i­ence in the area could open the door for Paul and oth­er mem­bers of Con­gress to re­as­sert them­selves and have more in­flu­ence.

“There was a time once in our his­tory when the Con­gress ac­tu­ally played an im­port­ant for­eign policy role, not merely as a crit­ic or snip­ing at the ad­min­is­tra­tion, but ac­tu­ally guid­ing U.S. for­eign policy,” said Chris­toph­er Preble, the vice pres­id­ent for de­fense and for­eign policy stud­ies at the Cato In­sti­tute. “I think there’s a real op­por­tun­ity there for Sen­at­or Paul.”