The Arizona Republican's attendance in the upper chamber Tuesday could be key in determining whether Senate Republicans are able to open the debate and amendment process on health care reform.

Senators will first vote Tuesday to proceed to the American Health Care Act (AHCA), the health care legislation that narrowly passed the House in early May. To advance to the next step, that will require 51 votes. If that's successful, Senate Republican leaders then expect amendments to be offered to that bill, a Republican aide told CBS News. With McCain's scheduled return, Republicans can only afford two defections on some of the major proposals, assuming Democrats stick together in opposition.

McCain, for his part, has advocated going back to the committee level and negotiating health care reform on a bipartisan basis.

The 80-year-old has been diagnosed with glioblastoma, an aggressive brain tumor, which was revealed to the public last week. It was discovered after he underwent a procedure to remove a blood clot above his left eye earlier this month.

source: AFP