Washington (CNN) Sen. Susan Collins told CNN on Wednesday she was "disappointed" that a bipartisan health effort collapsed while the Republican-only Graham-Cassidy bill surged ahead instead.

The Maine Republican has serious concerns about Graham-Cassidy but said she won't make her final decision until she sees a partial analysis of the bill from the Congressional Budget Office. That report is expected early next week.

So far, only one Republican -- Sen. Rand Paul -- has publicly refused to support the bill, and Republicans, who hold a 52-48 majority, can only afford to lose one more of their own to pass it with a tie-breaking vote from Vice President Mike Pence. If they lose two more Republicans, then there's no path for the bill as written to proceed.

All eyes are on Collins, as well as Sens. John McCain and Lisa Murkowski, who have also expressed deep reservations about the bill.

Collins said she preferred a push by the top Republican and top Democrat on the health committee -- Sen. Lamar Alexander of Tennessee and Sen. Patty Murray of Washington, respectively -- to help fix existing problems in Obamacare and stabilize insurance markets.

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