WASHINGTON - The Senate on Thursday evening was still staging a marathon voting session on the federal budget in which both parties looked to set themselves up to score political points for the 2016 election.

During "Vote-a-rama," as it's been dubbed, senators were working their way through amendment after amendment to a Republican budget proposal that GOP leaders were hoping to shepherd to final passage as soon as Friday. With their amendments, senators sought to draw attention to pet political causes, force others to weigh in on big debates and cause headaches for the other party.

"There's a lot of smoke and not a lot of fire," said Sen. Chris Murphy (D., Conn.). "So much of this is for show."

The politically charged votes could agitate both the presidential campaign and the battle for the Senate. Four Republican senators are either eyeing White House bids or have already launched them. Meanwhile, Democrats are trying to retake the Senate majority they lost in the 2014 GOP wave election mainly by targeting Republican incumbents up for reelection in blue and purple states.

Sen. Rand Paul (R., Ky.), whom many close watchers expect to soon launch a presidential campaign, introduced an amendment to increase defense spending by nearly $190 billion over the next two years, a notable move given Paul's libertarian leanings on national security. He proposed to cover the cost by trimming spending in other areas of the government.

Paul's amendment was rejected 96-4. But the vote could enable him to blunt charges in the Republican presidential primary that he is too soft on national security while protecting his fiscally conservative reputation.

The budget is a framework for the appropriations process, not a law. So the amendments are not part of a bill that will ever go to the president's desk. But they do offer a snapshot of what both parties believe to be good politics moving toward a pivotal election.

In the battle for the Senate, "Vote-a-rama" barbs were flying.

"Harry Reid Continues His Crusade Against Affordable Energy," declared a National Republican Senatorial Committee news release hitting the minority leader for voting against a Republican amendment that said it sought to establish a "deficit-neutral reserve fund to protect the United States from an energy tax." Reid (D., Nev.) is up for reelection in 2016.

The Democratic Senatorial Campaign Committee, meanwhile, issued a memo saying: "As we approach a slew of amendment votes on the budget in the Senate, one thing has been made imminently clear - vulnerable Republican Senators up for reelection in 2016 are running scared from their records of voting to end Medicare as we know it."

Some Republicans up for reelection in 2016 in swing and Democratic-leaning states voted with Democrats on an amendment from Sen. Patty Murray (D., Wash.) to enable Americans to earn paid sick time that would not add to the deficit.

Among them: Sens. Kelly Ayotte of New Hampshire, Richard Burr of North Carolina, Mark Kirk of Illinois, Rob Portman of Ohio, Pat Toomey of Pennsylvania, and Ron Johnson of Wisconsin.