The term "socialist" is an oft-used insult in U.S. politics, trotted out by conservatives to cast doubt on the economic credentials of almost any Democrat.

But while the likes of Bill Clinton and Barack Obama have strenuously denied the assertion, for the first time in a generation, there is someone running for president, in Vermont Sen. Bernie Sanders, who proudly claims that he is a socialist, while Sen. Elizabeth Warren, D-Mass., another leading contender, would also represent a significant lurch to the left for Democrats, even though she rejects the label.

But are either of them really socialists?

As a point of comparison, another election is taking place on the other side of the Atlantic, in the U.K., where the leader of the opposition Labour Party, Jeremy Corbyn, is also proud to say that he is a socialist.

Similar to Sanders and Warren, Corbyn has set his sights on the richest in society, whom he wants to pay more tax and help fund programs to reduce inequality.

Senators Bernie Sanders (left) and Elizabeth Warren (right) have dragged the debate in the Democratic presidential race to the left of the political spectrum. Source: AP Photo

Warren's proposals include a 2% tax of the wealth of people with assets of more than $50 million, while wiping out student debt of up to $50,000 for households with incomes below $250,000. Corbyn has pledged higher corporation tax, income tax increases for those earning more than £80,000 and taxing capital gains and dividends at income tax rates.

But there, the similarities end.

Nationalization

While both Warren and Sanders back Medicare for All, potentially upending the U.S. healthcare system, that represents a relative tinkering with the economy compared with Corbyn's plans. The Labour manifesto, released Nov. 21, includes pledges to nationalize rail, energy and water companies, and part of British Telecom, providing free full-fiber broadband to every home, as well as a plan to force companies to put 10% of their shares into an "Inclusive Ownership Fund," which would pay dividends to employees.

The left in both countries is looking to the past for inspiration, but their histories are very different, according to Kathleen Burk, professor emerita of modern and contemporary history at University College London.

"I do not think that the two categories [Democrat and Labour policy] are anywhere near," Burk said. "As far as what [Warren] is proposing has roots, they should be found in the New Deal and various anti-trust and financial regulations."

New Deal

Sanders has declared himself a socialist, but noted left-wing academic Noam Chomsky refers to him as a "new dealer," more in line with the policies of former U.S. President Franklin D. Roosevelt who instigated public works and social welfare programs that helped haul the U.S. out of the grips of the Great Depression.

Warren shares many policy goals with Sanders, but has repeatedly rejected claims she is a socialist, insisting that she is a capitalist and believes in markets.

"The fact that Sanders calls himself a socialist and Warren does not suggests that socialist/capitalist divide tells us less about policy than we might think and more about the valence assigned to the labels by different parts of the electorate," wrote E.J. Dionne Jr. and William Galston, fellows at the Brookings Institution.

British socialism

Labour party leader Jeremy Corbyn wants to return the U.K. economy to highly centralized model that was dismantled by Margaret Thatcher and Tony Blair. Source: AP Photo

In the U.K., Corbyn is trying to resurrect the post-war socialism of U.K. Prime Minister Clement Attlee (1945-1951) that led to increased state control of the economy, including the creation of the National Health Service in 1948, nationalization of some industries, including coal mining, and the formation of a welfare state.

But while the Labour Party were the dominant force in British politics after World War II, holding office for 17 of the following 25 years, for many Britons alive today, their last memory of a socialist administration was that led by James Callaghan (1976-1979). His government presided over the so-called Winter of Discontent of 1978/79, during which strikes by, among others, grave diggers, garbage collectors and NHS ancillary staff, caused chaos across the country and helped Margaret Thatcher (1979-1990) to power.

While Labour again took the reins from 1997 to 2010 under Prime Ministers Tony Blair and Gordon Brown, they abandoned socialism in favor of a "third way" that embraced markets and ploughed the increased wealth into services such as education, health and a minimum wage, policies more akin to administrations of Clinton or Obama.

Clause IV

Labour's shift to the center was symbolized by the removal of clause IV, a commitment to nationalization of industry introduced into the party's constitution in 1918, from the manifesto in the infancy of Blair's leadership.

Corbyn's stated willingness to consider reinstating Clause IV and roll back decades of economic liberalization has got pro-business groups worried.

Barack Obama, Hillary Clinton and Bill Clinton were at the heart of the centrist Democrat policies that dominated the party's recent history. Source: AP Photo

"Labour’s default instinct for state control will drag our economy down, rather than lift people up," said Carolyn Fairbairn, director general of the Confederation of British Industry.

The targets of proposed nationalization have also been taking action to protect shareholders against attempts by a Labour government to buy them out at below market value. Energy company SSE PLC last month moved its U.K. networks business into a Swiss holding company, while National Grid PLC’s UK business has been placed into holding companies in Luxembourg and Hong Kong, the Financial Times reported.

US socialism

The U.S., by contrast, has never seen a socialist government by any standard definition of the word. The closest it got was Eugene Debs who regularly ran for president, but never got closer than the 6% of the vote he secured in 1912. He spent his 1920 presidential campaign in prison having been arrested for an anti-war speech in 1918, a common fate for socialists opposed to World War l.

While the U.K. embraced collectivism in the post-war years, an increasingly muscular U.S. defined itself against communist Russia, resulting in the "red scare" that saw anyone with strong leftist tendencies labeled a traitor.

For now, though, the centrism of the 1990s and early 2000s appears dead on both sides of the Atlantic, with Blair seen as toxic by many for his promotion of U.K. involvement in the Iraq war and the Clintons vilified for their close relationship with Wall Street and other wealthy interests.

"In the U.S., U.K., and elsewhere, insurgents have rejected what they see as the Third Way’s objectionable and ineffective compromises with conservative principles and programs," said Dionne and Galston from Brookings.