WASHINGTON – When Sens. Susan Collins and Olympia Snowe broke ranks with GOP leadership last week and joined three fellow Republicans in voting against the House GOP’s budget plan for the next fiscal year, you could almost hear the chant from their right flank.

R-I-N-O was the cry, the derisive term that is used by conservatives to describe those they consider “Republicans In Name Only” and is often hurled at Snowe and Collins.

But there was a similar gnashing of teeth from liberals May 19, when Snowe and Collins joined all but one Republican senator in voting to filibuster the nomination of Berkeley law professor Gordon Liu, President Obama’s nominee for the 9th U.S. Circuit Court of Appeals.

The left said it broke with the Maine Republicans’ longstanding promises not to use the filibuster to block judicial nominees from receiving final Senate votes, and showed that they caved under pressure from the right wing.

Ignored was the fact that, just a couple weeks earlier, Snowe and Collins had taken their more normal stance and joined nine other Republicans in voting to break the filibuster by GOP leadership of a federal district court nominee, John McConnell of Rhode Island.

Getting lashed from the left and the right is par for the course for Snowe and Collins, and many other moderates.

And despite increasing partisan polarization in the Senate — which more and more resembles the House and its procession of party-line votes — Snowe and Collins are continuing to hew to a pretty moderate line this year, analysts say.

The big question has been how Snowe would respond to a potential tea party challenge looming next year, when she will be up for re-election. Was Snowe’s vote to back tea party favorite Sen. Rand Paul in his bid to challenge the constitutionality of President Obama’s decision to launch military action against Libya an example of pandering?

After all, no Democrats and just 10 Republicans, most of them hard-line conservatives, voted in April for Paul’s resolution quoting then-Sen. Obama’s 2007 statement that a “president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.”

Or was Snowe’s vote a way for her and Collins to register their objections to Obama’s handling of Libya and their unhappiness with the president not coming to Congress for permission?

Did Snowe and Collins undermine their moderate reputations earlier this year when they voted for a procedural motion to allow the House GOP bill that sought to cut $61 billion from the remainder of 2011 spending to come to the floor for a final vote?

Did that vote mark them as supporting all the cuts in the bill, which failed? Or, despite their criticism of some of the cuts, was it the only way they saw to protest what they viewed as a lack of responsible 2011 spending options being presented by either party for a vote?

Jennifer Duffy, who tracks the Senate for the nonpartisan Cook Political Report, said Snowe and Collins are “staying pretty true to their moderate roots. In Snowe’s case, there is a sensitivity there to issues that the tea party cares about, but I don’t think you are seeing a big change in overall voting behavior.”

That seems to be born out this year by “party unity” voting statistics, the percentage of votes in which a senator votes with the majority of his or her party.

As of Friday, Collins had voted with the GOP majority on 83 percent of the votes this year, while Snowe had done so 86 percent of the time, according to a database compiled by the Washington Post.

That may seem like a pretty loyal voting record, until it’s put into context.

Fifty-six senators have voted with their party 95 percent of the time or more so far this year. Just 16 have voted with their party 89 percent of the time or less, and just 10 senators have voted with their party 86 percent of the time or less.

Over time, Snowe and Collins have voted “their consciences and moderate positions although in the zero-sum world of today’s Washington, partisans on the far left and the far right demand ideological purity,” said Christian Potholm, a professor of government at Bowdoin College.

“Maine voters, since 1948 and even before, have almost always prized and rewarded independence and moderation.”

Asked whether Snowe and Collins are about as moderate as it gets in the Senate these days, Potholm responded, “Yes, unfortunately. The answers and solutions to America’s many national problems lie in the middle of the political spectrum.”

Gone from the Senate over the past few years are moderates from both parties, Republicans such as Gordon Smith of Oregon and George Voinovich of Ohio and Democrats such as Evan Bayh of Indiana and Republican-turned-Democrat Arlen Specter of Pennsylvania.

One reason for increasing party unity is increasing numbers of procedural motions, which tend to draw more partisan votes even from moderates.

“Many of these votes now are not just the vote on final passage, but lots of procedural votes that come with that, and that tends to buck up party support scores,” said Anthony J. Corrado, a professor of government at Colby College.

“In terms of Snowe and Collins, it is clearly the case that they remain firmly amongst the more moderate senators.”

MaineToday Media Washington Bureau Chief Jonathan Riskind can be contacted at 791-6280 or at:

jriskind@mainetoday.com