Senate Republican leader Mitch McConnell of Kentucky challenged threats by Democratic leaders to change the filibuster rules because of the delays, pointing to Reid's earlier promises not to take such a step. In 2009, Reid told reporters it would "ruin our country" to alter the rules. A change in the rules could leave Democrats on the losing side if party control of the chamber shifts and a Republican president is pushing nominees through the chamber, McConnell said. "We know that majorities of either party will never get everything they want," he said on the Senate floor. "That push and pull is the hallmark of a healthy democracy. And one day, when they are invariably returned to the minority, I suspect my Democrat friends will thank us for standing up for these democratic rights." McConnell and other Republicans said Democrats are exaggerating the matter, because the Senate has confirmed other nominees, including Obama's selections to lead the Commerce and Transportation departments, and to head the White House Office of Management and Budget. Most of Obama's judicial nominees for federal courts also have been confirmed, lawmakers said. "The important thing to realize is that all of the president's nominees have been considered in almost embarrassingly fast speed," said Sen. Lamar Alexander, R-Tenn. "As far as judges go, there's almost no one left to confirm." The clash over Perez threatens the Senate tradition of avoiding filibusters when considering Cabinet appointees. In February, Republicans staged a filibuster on the nomination of Chuck Hagel as Defense secretary, only the third time a Cabinet pick needed 60 votes to overcome delaying tactics, said Betty Koed, the Senate associate historian. President Ronald Reagan's 1987 pick for Commerce secretary, C. William Verity, and President George W. Bush's 2006 choice of Dirk Kempthorne to be Interior secretary also faced filibusters. Like Hagel, both overcame the obstacle to win confirmation. Some Republicans say they haven't decided whether they would vote to affirm a filibuster to obstruct the nominees, or whether they might merely vote against them in a final vote in which confirmation requires a simple majority of the Senate's 100 members. Those still making up their minds on the procedural matters include Alexander, the top Republican on the Senate's labor panel, as well as Pat Roberts of Kansas, who also serves on that committee. Both say they oppose Perez. Perez, now the Justice Department's top civil rights lawyer, has drawn Republican criticism for his handling of two whistle-blower lawsuits that the department declined to pursue. They were part of a deal in which St. Paul, Minn., officials agreed to drop a case being appealed to the Supreme Court in return for the department withdrawing from the other cases. The Supreme Court case risked striking down an enforcement tool used in housing discrimination cases. At his April confirmation hearing, Perez clashed with Republicans over the lawsuits. McConnell fueled growing partisan opposition by calling Perez a "crusading ideologue" with a history of twisting the law to win desired outcomes. In McCarthy's case, her detractors said their opposition focuses on the agency's actions rather than her qualifications. Sen. David Vitter of Louisiana, the top Republican on the Environment and Public Works Committee, said Tuesday he would not support a filibuster against McCarthy after he had "very productive conversations" with agency officials. He complained last month that the EPA refused to fully answer questions he posed about the agency's transparency in developing and analyzing clean-air rules. McCarthy is the EPA assistant administrator for air pollution. Her confirmation may be complicated by Obama's plans, outlined last month, for a package of initiatives to curb greenhouse gas emissions, including the first limits on carbon emissions from all power plants. Such a move is opposed by utilities such as Southern Co. and coal producers including Peabody Energy Corp. Senate Republicans, including John Barrasso of Wyoming, said Obama's plan may hurt McCarthy, who testified that an emissions rule affecting existing coal-fired power plants wasn't in development. Barrasso said on the Senate floor June 25 that McCarthy is "either arrogant or ignorant." Democratic senators seeking re-election in 2014 in states that voted for Republican presidential candidate Mitt Romney last year are under pressure to split with the party on votes tied to Obama's climate-change announcement. The National Republican Senatorial Committee sent statements about Obama's "radical climate change agenda" to news organizations in states where Democratic senators including Mark Pryor of Arkansas, Mary Landrieu of Louisiana and Kay Hagan of North Carolina face re-election. Romney carried all three in the 2012 presidential election. Landrieu said in an interview yesterday that she is leaning toward supporting McCarthy, in part because she is backed by industry groups representing businesses regulated by the EPA. "I've met with her and she seems very reasonable and moderate," Landrieu said. "I'm not happy with the EPA generally, but somebody needs to run it. And she's probably going to be the most business-oriented nominee we could get out of the administration." McCarthy allies including the Sierra Club and the League of Conservation Voters have formed a coalition, SaveOurEnvironment.org, that is running web ads and a blog on the website of the Washington Post defending her record. "McCarthy has worked for both Republicans and Democrats in key posts directing environmental and public health policies," the coalition wrote in a blog item. "In fact, Republican and Democratic senators already easily confirmed McCarthy by a voice vote during her last confirmation for head of the clean air division of EPA." Senate Environment and Public Works Committee Chairman Barbara Boxer said she's convinced McCarthy can overcome objections and win confirmation. Boxer said that's partly because McCarthy has a history of bipartisanship that includes serving as an environmental adviser under five Massachusetts governors that include former Republican governor William Weld. Boxer, D-Calif., also said that while Reid could try to change Senate rules over the confirmation feud, she sees him as wary of doing so. "He would much prefer to run this place in a collegial way and let the president have his team in place," said Boxer. "If he can avoid changing the rules, I think he will."