U.S. Senator Arlen Specter's decision to defect from the Republican Party and become a Democrat is the latest setback for a party still reeling from national election defeats in 2008 and 2006.
Political survival appears to be the immediate reason for Senator Specter's party switch.
Specter acknowledged his prospects in a Republican primary in his home state of Pennsylvania next year were bleak because tens of thousands of moderates have left the Republican Party in that state and joined the Democrats.
"As the Republican Party has moved farther and farther to the right, I have found myself increasingly at odds with the Republican philosophy and more in line with the philosophy of the Democratic Party," said Arlen Specter.
Specter also noted a trend in recent years in which conservative Republican candidates have targeted moderate incumbents in primary elections.
"They do not make any bones about their willingness to lose the general election if they can purify the party. I do not understand it but that is what they say," he said. "There ought to be a rebellion. There ought to be an uprising."
Senator Specter's conversion is welcome news for Democrats. They are one step closer to securing 60 of the 100 U.S. Senate seats. That would make it harder for Republicans to block President Barack Obama's legislative proposals in the Senate through a parliamentary delaying tactic known as the filibuster.
President Obama welcomed the Senate's newest Democrat to the White House (Wednesday).
"In fact, I would like to think that Arlen's decision reflects the recognition that this administration is open to many different ideas and many different points of view, that we seek cooperation and common ground," said President Obama.
Specter's defection caught many Republicans by surprise. It is the latest in a series of political setbacks for a party that lost control of Congress in the 2006 midterm elections and lost the White House last November.
Many Republicans sought to minimize the national political fallout from the Specter defection.
Former Senator Fred Thompson of Tennessee said on his radio show that Specter was always out of step with the conservative wing of the Republican Party.
"I would feel a little better about it if he would just acknowledge that, 'Folks, I think I am going to get my fanny beat if I go down this trail and I want to stay around here," said Fred Thompson.
Senate Republican leader Mitch McConnell of Kentucky said Specter's decision was not a national story, but a Pennsylvania story, and said Republicans are eager to do battle in the next congressional midterm elections in 2010.
"We intend to be competitive on a nationwide basis," said Mitch McConnell. "I do not accept that we are going to be a regional party, and we are working very hard to compete throughout the country."
But Democrats do see national implications in the Specter decision.
John Podesta was White House chief of staff for former President Bill Clinton and now heads a liberal public policy research organization in Washington.
"Certainly his decision to leave the Republican Party should be a warning shot, I think, to the leadership in Congress in particular that they have just careened too far off to the right and have left the middle behind," said John Podesta.
Political experts say there are things the Republican Party can do to improve their political prospects before next year's congressional elections.
Stephen Wayne is a presidential scholar at Georgetown University in Washington.
"The Republicans need to broaden their electoral base," said Stephen Wayne. "In the last couple of elections they have lost, by sizable margins, the support of young people, first time voters, Hispanics, and women."
Even some Republicans say the party needs to adjust its message and attitude to be more appealing.
Ken Duberstein served as former President Ronald Reagan's chief of staff in the late 1980's, but he endorsed Barack Obama in last year's presidential election.
"They need to be very much positive," said Ken Duberstein. "It is the shining face of Ronald Reagan. It is not the 'just say no' that seems to be dominating the Republicans now. You know, you have to be perceived as interested in governing, not just campaigning."
Duberstein also worries that Republicans are a disappearing political breed in the Northeast, and will have to rely on a shrinking base of support primarily in the South.
"The Republican Party can offer an awful lot, but they have to do that by reaching out, not just to the South or some places in the Midwest, but to contest again in the Northeast and in the West Coast and in the Southwest," he said.
The Democrats may be celebrating now, but experts warn that political fortunes can turn very quickly.
The last time Republicans held only 40 Senate seats was following the election of 1976. But four years later, Republicans captured 12 seats and won a majority in the Senate. It was the same year Ronald Reagan was elected president, and it was also the same year a newcomer named Arlen Specter was elected to his first Senate term in Pennsylvania.