Democrats set final passage of the most extensive Veterans Affairs benefits expansion in decades after rejecting a GOP attempt to make the measuring mirror a Senate-passed bill that Republicans had said might arrive on Joe Biden's desk this week.

Rep. Mark Takano, D-Calif., the House Veterans’ Affairs chairman, expects the bill to pass Thursday. It will overhaul the VA's health care system for veterans exposed to toxic chemicals during their tours of duty.

Even so, it is unclear whether the 50-50 Senate will take up the measure anytime soon, despite intensive lobbying and passionate appeals from veterans advocates.

The House bill addresses the long-standing debate over whether it can be assumed that a veteran became ill after service in the military, whether it was through exposure to Agent Orange in Vietnam, oil well fires during the Gulf War, or open-air burn pits during the Afghan campaign.

Rather than having the VA specify which illnesses are service-connected and review the individual veterans' status in a cumbersome manner, the bill would declare several respiratory diseases and cancers service-connected and eliminate the burden of proof from veterans.

The legislation would presumptively connect Agent Orange exposure to hypertension and Monoclonal Gammopathy of unknown significance, which can sometimes progress to blood cancers in more than a half-million Agent Orange-exposed Vietnam veterans.

Veterans who served during specific periods in certain regions may be eligible for hospital care, medical services and nursing home care after a phase-in period.

A series of conversations with White House staff led to Biden giving the bill a boost during his State of the Union address before the House debate. In addition, it was on Biden's mind since his son Beau, who served alongside him in Iraq, died of brain cancer; he suggested the disease might have been caused by exposure to burn pits.

In a news event on Wednesday, Speaker Nancy Pelosi said that it's like a sliver of Washington D.C. It took the president weeks to work on it."

The House bill is also quite costly: According to the Congressional Budget Office, direct benefits for disabled individuals would increase by $208 billion over a decade. Added to that is the cost of new health care benefits, which are paid for through appropriations, plus VA admin costs.