Washington Election Results

So powerful was the SNP tide that among those swept away was Douglas Alexander, ­Labor’s shadow foreign secretary and campaign chief, who lost his seat to a 20-year-old student. Conceding defeat, Alexander said it is now Labor’s “responsibility to re-win the trust” that had obviously been lost.

Later, Jim Murphy, the leader of the Labor Party in Scotland, also lost his seat to the SNP. And an incredible 35-point swing toward the SNP cost Labor the seat long held by former prime minister Gordon Brown, who had decided to retire.

A confluence of events brought Scotland and the Labor Party to this moment, some reflecting long-standing problems within the party and others triggered by reaction in Scotland to the referendum campaign. Rather than contracting after losing the independence vote, the SNP was revitalized, with a sharply increased membership and an enthusiasm unmatched by the Labor Party.

During the independence referendum campaign, Labor made what appears to have been a costly decision to join the Conservatives and others in a cross-party effort to preserve the United Kingdom and defeat the movement to break away. To voters who want a Labor Party devoted to Scotland, the decision looked like a betrayal — a party in league with London that was no longer authentically Scottish.

“There was a feeling [in Scotland] of ‘they sold us out, ’ ” said Peter Riddell, director of the ­London-based ­Institute for ­Government.

The second factor was the ­neglect of the Labor Party in Scotland by its national leaders, a ­disregard that has long stirred resentment. For years, talented Labor leaders from Scotland headed to London and the national government. The national party was looking to Scotland principally as a source of seats to buoy its strength in Parliament, rather than acting as an advocate for Scotland, analysts here said.

Meanwhile, the party in Scotland was atrophying, with membership declining sharply and its local organizations weakened by complacency. By this spring, it was clear that Labor in Scotland was a hollowed-out ­party with little muscle to wage an effective campaign. But that hollowing was two decades in the making.

“We had a false result in 2010 where people voted for [former prime minister] Gordon Brown because he was a Scot, ” said Paul Sinclair, a former Labor adviser. “While the SNP consistently modernized and became a very modern professional outfit, the Labor Party just withered on the vine.”

The third factor has been the performance of SNP leader Sturgeon, who emerged as the undisputed star of the campaign this spring as she traveled around Scotland in a helicopter adorned with her photograph. She delivered strong performances in televised debates and forums. She also lacks the hard edges of former leader Alex Salmond, who was either loved or loathed.