Senators gave tacit blessing to president Barack Obama’s strategy for fighting the Islamic State on Thursday, overwhelmingly passing a budget bill that also granted him authority to arm and train rival Syrian rebel groups.

Despite attempts by Senator Rand Paul to separate the Syrian authorisation from the wider bill on the grounds that it deserved a separate debate, just 27 senators stood in the way of the cloture motion which allowed Obama to avoid a potentially embarrassing direct vote.

Paul claimed the bill, which finally passed by 78 to 22 represented a “sad day for the US Senate” and also criticised the underlying strategy of arming groups which he claimed had little interest in fighting the islamic extremists known as Isis.

“It’s not that I’m against all intervention, I do see Isis as a threat to us – but I see our previous policy as having made it worse,” said Paul. “There are valid reasons for war. They should be few and far between. … They should not be [hidden] in the pages of a 1,000-page bill and shuffled under the rug.”

Several Democrats standing for re-election in November’s midterms such as Mark Begich of Alaska also spoke out against the Syria authorisation, and were joined by Elizabeth Warren of Massachusetts, Joe Manchin of Philadelphia and Patrick Leahy of Vermont in voting against the bill.

But the bill was backed by both Republican and Democratic party leaders and will now be signed into law by Obama having cleared more significant opposition in the House of Representatives on Wednesday.

Florida senator Marco Rubio was one of several mainstream Republicans who spoke reluctantly in favour of Obama’s strategy. “The options before us now are not as good as they we had done this two years ago. But today we are called on to decide what to do now,” he said. “That means better late than never.”

Arizona senator John Mccain, who pushed for the groups to be armed two years ago, said it was “long overdue” but may no longer prove decisive in the face of more than 33,000 Isis fighters.

But Paul returned to his anti-interventionist stance that may prove the centrepiece of his anticipated 2016 presidential campaign with a blistering speech against the bill.

“These barnacled enablers [in Washington] have never met a war they didn’t like … but intervention created this chaos,” he said.

“We’re in the middle of a three-way war, fighting alongside jihadists,” he added. “Think about the insanity of this … we need to stay the heck out.”