Story highlights Sen. Rand Paul is planning to unveil Obamacare replacement legislation in the coming days

Republicans are using a fast-track budget mechanism to repeal major portions of the law

Washington (CNN) Republicans are preparing to take a major vote this week aimed at repealing Obamacare -- but the drumbeat of concern within GOP ranks about the lack of a replacement is growing louder.

The Senate is poised to vote on a budget resolution later this week, the first in a two-step process of rolling back major parts of the Affordable Care Act. At the same time, GOP lawmakers are speaking out with force, concerned about the political backlash if the GOP is perceived as being reckless given that 20 million Americans have health coverage through Obamacare and there's no clear vision or firm timeline for an alternative.

These early concerns indicate swelling reservations over what's become known as the GOP's "repeal and delay" strategy -- voting on repeal but delaying the repeal from going into effect for several years, buying the party time to craft a replacement plan.

Sen. Bob Corker warned fellow Republicans that it would be "problematic," "not very appealing" and "doesn't seem very intelligent" to repeal the law without a replacement.

"To me, it's much more prudent to figure out where you're going to go from here, and attempt to do it all at the same time," the Tennessee Republican told CNN. "People will see some of the flaws in just repealing only."

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