WASHINGTON » Of the multitudinous insults that have zinged across the Capitol this year, a taunt most brutal was leveraged by the Republican leader, Sen. Mitch McConnell of Kentucky, on the Senate floor Thursday night. He accused the Democratic leader, Sen. Harry Reid of Nevada, of "fundamentally turning the Senate into the House."

McConnell’s rage — and its expression roughly akin in this town to comparing the Hope diamond to a Joan Rivers baguette sold on cable TV — stemmed from a last-minute tweaking to the Senate’s intricate rules that prevented Republicans from forcing Democrats to vote on a stream of unrelated amendments to a China currency bill.

One of the measures was to bring up President Barack Obama’s jobs bill, which Republicans said they believed they could defeat.

The change, which hamstrung McConnell and marginalized Republicans on a bipartisan bill, set off a remarkably pointed exchange between the two leaders on the Senate floor, a culmination of sorts of months of bitter wrangling in the Senate, where little had been accomplished.

The procedural change was as convoluted as it was incendiary. In a rare move, Republicans and Democrats in the Senate this week agreed to move forward on a trade bill aimed at the Chinese, who have been accused of manipulating their currency. Under the Senate rules, once the chamber has agreed to end debate on a bill, there is no chance for unrelated amendments to come to the floor.B

But the Republicans moved Thursday to get around the rules; they wanted to offer several unrelated amendments, including a politically charged vote on the jobs bill.

The presiding officer ruled the motion in order. But Reid held a vote to overturn that ruling, which passed 51-48, with all Democrats but Sen. Ben Nelson of Nebraska voting for it. The result was that a Senate precedent was set in which motions to suspend the rules — to offer unrelated amendments — after the Senate had agreed to end debate on a bill would no longer be permitted.

The Senate often makes precedents — there are more than 1,000 pages of them in the Senate procedure book — which define the rules, and they come and go. As a matter of legislative consequence, the precedent is not hugely significant. Few senators move to suspend the rules with a vote after debate has ended on a bill; the last such effort to succeed was in 1941.

But this move underscored the partisan hostility in the Senate on the eve of a big election year and could make it harder to get a polarized Senate to move forward on bills, said Martin Paone, a former Senate Democratic secretary and now executive vice president of Prime Policy Group, a lobbying firm.

"The minority is chafing at the fact that there hasn’t been an open amendment process in a long time," he said.

The change attracted strong feelings because it reflected each party’s central gripe.

"The fundamental problem here is the majority never likes to take votes," said McConnell, his voice rising from the Senate floor. "The price of being in the majority is you have to take bad votes."

A desire for vigorous debate is why people run for the Senate, not the House, McConnell said.

"They wanted to be able to express themselves." He added: "This is a free-wheeling body, and everybody is better off when we operate that way." (The House does most things by majority rule, and the minority has very little voice.)

Reid, who has time and again been hornswoggled by McConnell’s parliamentarian moves, countered that the problem was Republicans slowing bills and sometimes killing them with procedural tricks. (Most recently, McConnell refused to give unanimous consent to allow the Democrats to fix a typo in a short-term measure to fund the government.)

"This is not the way to legislate," Reid said. "We have to make the Senate a better place," and the best way to do so, he added, is to "do what was done tonight and get rid of these dilatory amendments."

On Thursday evening, senators filled into the chamber, voting along party lines on Reid’s new precedent. Reporters watched riveted, from the gallery.

"For me, having been there that long, it was like reality TV," said Paone, who caught the action on C-SPAN.

Reid could be seen browbeating Nelson and in a somewhat agitated conversation with Sen. Claire McCaskill, D-Mo., one of the last to vote. The Senate then became vaguely "West Side Story," with enraged Republicans on one side of the chamber, snorting at times in disgust as Reid spoke, while Democrats stood near their leader, some with clenched hands.

After all the fuming, McConnell, Reid and all members present agreed to put off their vote on the China bill until Tuesday.