This was a vote to begin formal consideration of the resolution. Under the Congressional Review Act, the Senate must first vote to "proceed" to the measure before they can debate it or hold a final vote on whether to pass it.

The resolution remains on the Senate calendar, but without a successful motion to proceed, it is unlikely to advance further. The EPA's disapproval of the Colorado air plan stands.

This vote highlights the conflict between state-led environmental plans and federal oversight. It specifically impacts how smog and visibility are regulated in Colorado's iconic natural areas.

• Colorado Environmental Agencies
  They must now deal with the EPA's rejection of their haze-reduction plan rather than moving forward under their own preferred strategy.
• Industrial Facilities in Colorado
  Businesses contributing to air pollution may face stricter federal requirements if the EPA imposes its own plan.
• National Park Visitors
  Future air quality and visibility in scenic areas like Rocky Mountain National Park depend on whether the federal or state plan eventually takes effect.

The vote was entirely split along party lines, with Democrats supporting the start of the debate and Republicans blocking it.

Motion to proceed

Senate motion to begin formal floor consideration of a bill. Itself filibusterable, so often the first hurdle a bill faces — and often where bills die without ever being debated on their merits.

Cloture

Senate procedure that ends debate on a measure. Requires 60 votes to invoke on most legislation, simple majority on nominations after the 2013/2017 nuclear options. Voting yes on cloture is not the same as voting yes on the underlying bill — many senators do one but not the other.