The Senate on Thursday again voted to reject two measures related to the Keystone XL pipeline that declared that humans are a cause of climate change — the second set of votes on the issue in two days.

Senators are using the Keystone debate to argue over climate issues. The Democrats want to force their Republican colleagues to come out one way or another on whether they believe humans have a role in changes to the climate and the rise of global temperatures. Republicans telegraphed their intent to attack President Obama’s climate policy agenda.

Mr. Obama is expected to veto the underlying bill that would force federal approval of the Keystone pipeline and allow construction to begin. Still, the debate has led to the first Senate floor votes in eight years on climate change measures.

On Thursday, the Senate voted 56 to 42 not to take up an amendment offered by Senator Bernard Sanders, independent of Vermont, that declared that climate change is real, is caused by humans and wreaks devastation. The amendment also called on the federal government to lead the way in the national transition away from dependence on fossil fuels.