But tax reform is "not the whole ball game," strategist Bob Doll tells CNBC.
Johnson says President Trump personally promised to "'work my tail off'" to win the Wisconsin Republican's vote.
"In the current form, I wouldn't vote for it," the Wisconsin Republican says.
Sen. Ron Johnson, (R-Wis.), talks about his opposition to the current version of the Senate's tax bill.
Sen. Collins is back in the spotlight as a swing vote in the Senate as she questions combining a Republican tax-cut plan with a partial repeal of Obamacare.
Johnson is the first GOP senator to explicitly say he will not back the tax proposal.
U.S. stocks closed lower on Wednesday as the current bull market showed signs of slowing down.
"I was trying to first of all defend John's position," Wisconsin Sen. Ron Johnson tells CNBC.
Wisconsin Sen. Ron Johnson suggested fellow Republican Sen. John McCain's brain tumor and late-night timing affected his vote against the health care bill.
On health care reform. Republicans are looking for at least 50 votes to pass Obamacare overhaul, Vox reports.
Upward of a dozen Republicans oppose the bill drafted by Senate Majority Leader Mitch McConnell, Vox reports.
Republicans can afford to have no more than two members of their Senate caucus defect if they hope to pass a new health-care reform bill.
Four Republican senators announced they will not support the Senate's current Obamacare replacement plan and will push for changes.
Wal-Mart, the big-box behemoth, is both the U.S.'s largest private sector employer and a lightning rod for controversy.
In the retail world, many are trying to stand out against Amazon, but former J.C. Penney CEO Ron Johnson says only one is truly making an effort.
'Repeal and replace' Obamacare is a 'fun buzzword,' but it's not realistic, Sen. Ron Johnson tells CNBC.
Sen. Ron Johnson, (R-Wis.), talks about the complexities of repealing and replacing Obamacare.
Sen. Ron Johnson, (R-Wis.), shares his thoughts on the strong U.S. dollar and economic growth.
Sen. Ron Johnson tells CNBC he has not seen the evidence of Russian-led election hacking, but says such moves would not be surprising.
Sen. Ron Johnson (R-Wis.) talks about the top issues President-elect Trump needs to address as soon as he takes office, including rolling back regulations and repairing Obamacare.