Does the US need a third party, and can one succeed? According to the founders of the new Forward party, the answer to both questions is yes. By targeting disaffected Americans on all parts of the political spectrum, the founders – who include the former Democratic presidential candidate Andrew Yang and the former Republican governor of New Jersey Christine Todd Whitman – hope to create a new force that will lead Americans into a future in which they can “cut out the extreme partisanship, reintroduce a competition of ideas, and work together in good faith”.

Sounds great. But unfortunately, the Forward party is ill conceived, based on a faulty idea of how to fix America’s descent into political madness, and likely to collapse under the weight of its own contradictions.

At the core of the party’s justification for its own existence is the suggestion that both of America’s two major parties are to blame for the country’s dysfunction, and that the only way to move forward is to replace them with something new. This is a misleading and self-serving diagnosis. Whatever gripes one might have with its policies, the Democratic party is the only one of the two major parties committed to basic democratic and liberal norms. The problem that ails America is that Republicans are not.

The absurdity of this attempt to create a false equivalence becomes even clearer when the new party’s founders talk details. They argue that “most Americans” agree neither with “the far right’s insistence on eliminating gun laws” nor with “calls from the far left to confiscate all guns and repeal the Second Amendment”. But these two things are not the same: the first is what is actually happening in America right now, whereas the second is a view that was attributed to Kamala Harris as part of a fabricated smear on Facebook and enjoys approximately zero support in the Democratic party.

On abortion, the party’s founders similarly contrast “the far right’s quest to make a woman’s choice a criminal offence” with “the far left’s extreme views on late-term abortions”. Once again, the false equivalence is startling. It’s thanks to the mainstream Republican party, not the “far right”, that abortion is now illegal in eight states, with many more expected to follow. “Late-term abortion”, meanwhile, is a medically meaningless term used by conservatives to imply that women who have life-saving surgery late in their pregnancy are in fact having elective abortions, cheered on all the way by baby-killing liberals.

When they avoid talking specifics, the founders can sound more convincing. Who could disagree with “welcoming new ideas” and “creating a political home” for people from both parties? But in the America of today such bromides feel – to borrow, in the spirit of bipartisanship, a phrase from Sarah Palin – “hopey-changey”. In reality, there is only one responsible place for anyone to be if they want to protect America’s democratic, liberal norms – and that place is in the Democratic party.

Instead of strengthening this one last realistic defense that the US has left, the Forward party will weaken it. The party’s founders draw on old polling data from just after the January 6 insurrection to claim that 50% of Americans now identify as independents. In fact, the figure is now nearer 40%, and political scientists will tell you that there are very few “true” independents in America’s polarized political landscape. Of that small pool, the Forward party – whose most recognizable face is Andrew Yang, a former Democrat – seems much more likely to siphon votes from the left than from the right. Even if it doesn’t, it will have helped spread propaganda about liberals wanting to end the second amendment and legalize third-trimester abortion, benefiting Republicans. Even a small electoral effect could spell disaster – especially with Republican state governments poised to steal close elections in swing states.

The final problem with the Forward party is its internal incoherence. The party promises “common sense” solutions, but common sense means very different things to different people. The fact that the party is trying to stitch together supporters from across the political spectrum is probably one reason it is offering so few details about what its actual policies will be. Political tents can only get so big before they collapse under the weight of their own contradictions, and it is hard to see how the Forward party can avoid a similar fate if it wants to move beyond platitudes.

The Democratic party may not be perfect. But the two-party system, and the threat to America’s democracy posed by Republicans, has a stark and brutal logic. Those who care about democracy and liberalism should advance the cause of the Democratic party. Republicans who cannot bring themselves to do that should work to change the Republican party from within. Anything else is a vanity project. Such projects might have value to politicians who had their personal ambitions thwarted in the regular party system. But what do they possibly have to offer the American people?

• Andrew Gawthorpe is a historian of the United States at Leiden University and host of the podcast America Explained