Sen. Bob Corker (R-TN) joined the small but growing chorus of Republicans declaring their discomfort with the current GOP plan of repealing Obamacare in the weeks to come without a replacement.

“Repeal and replacement should take place simultaneously,” Corker said Friday, according to Bloomberg News.

Three other senators have publicly said they would like to repeal Obamacare with some sort of replacement ready, putting the margin Republicans will need to pass a repeal-only bill in the upper chamber in danger. With the GOP holding only 52 seats in the Senate, and Democrats unified in their opposition to repeal, Republicans can afford to lose only a few votes in their repeal effort.

This week, both Sens. Tom Cotton (R-AR) and Rand Paul (R-KY) expressed their objections to the repeal-only approach, while Sen. Susan Collins (R-ME) has been skeptical of the approach since early on, and even voted against the 2015 “test run” legislation that repealed Obamacare but was voted by President Obama.