WASHINGTON — After months of heated negotiations, a bipartisan group of eight senators finally achieved compromise, coming together to unveil a broad overhaul of the nation’s immigration laws. But at a Senate Judiciary Committee hearing on the legislation Monday, a new set of divisions began to emerge, offering an early glimpse at the partisan politics likely to be on display as the immigration bill winds its way through the Senate.

At the marathon session, which featured testimony from 23 people, both lawmakers and witnesses raised charged questions. Could an immigration overhaul be done in separate pieces, without including a path to citizenship? What protections, if any, do same-sex couples deserve? How should the Boston bombings affect the immigration debate? The tempers of legislators flared, and at one point the hearing needed to be gaveled back to order.

Senator Patrick J. Leahy, Democrat of Vermont and the chairman of the committee, took issue with conservative commentators and Republican lawmakers who suggested that any debate about an immigration overhaul should take into account that the two suspects in the Boston bombing emigrated to the United States from Kyrgyzstan.

“Last week, opponents of comprehensive immigration reform began to exploit the Boston Marathon bombing,” Mr. Leahy said. “Let no one be so cruel as to try to use the heinous acts of these two young men last week to derail the dreams and futures of millions of hard-working people.”