The Defund Obamacare movement has lost another key conservative senator.

Kerry_Nomination_0f3c4_image_1024w Sen. Ron Johnson (AP Photo/J. Scott Applewhite)

Sen. Ron Johnson (R-Wis.), in comments to the Milwaukee Journal Sentinel, echoed other Republicans who have said it's not a practical strategy to threaten not to fund the government unless the president's health care law is stripped of its funds.

"Even if we were to not pass the continuing resolution [to fund the federal government], you're not going to be able to defund Obamacare, absent of President Obama signing a law, which I think is highly unlikely," Johnson said. "So I appreciate the fact that they've raised the issue. But defunding Obamacare, with President Obama in the White House and Harry Reid in the Senate, I think is next to impossible."

Johnson regularly aligns with the conservative wing of the party, several of whose members -- including Sens. Mike Lee (R-Utah), Ted Cruz (R-Texas) and Marco Rubio (R-Fla.) -- are leading the defunding effort.

Conservative GOP Sens. Tom Coburn (Okla.) and Richard Burr (N.C.) have also distanced themselves from the proposal.