An ambitious Biden's margin for error or bad luck is close to zero

US President Joe Biden has breathtaking ambitions. The $1.9 trillion pandemic relief bill is the most far-reaching legislation in 50 years to redirect assets to the poorest Americans, especially children. And he intends to go far beyond that spectacular start.

He is now promoting a massive $2tn infrastructure and climate change package. Securing that means operating at the Franklin Roosevelt-level of historic significance.

Since the 1960s, Democrats mainly emphasised social spending. Republicans have mostly promoted the interests of corporations and the wealthy. Both robustly fund the military and serve the special interests that support them.

Suddenly here is a major federal initiative for the country as a whole, the basic infrastructure of the US.

It goes far beyond traditional definitions of "infrastructure", although it does provide considerable spending on roads and bridges, railways and public transportation, schools and affordable housing. Yet there are also vast investments in home and community care, universal high-speed broadband, the power grid, cleaner energy and electric vehicles.

Critics see a liberal laundry-list grab-bag, especially since the plan will supposedly be primarily funded through tax increases on corporations and the wealthy, effectively reversing former US president Donald Trump's 2017 tax cut. It would be another huge step in rearranging social and economic relations in the interests of ordinary people at the expense of corporations and the wealthy. And it would transform significant aspects of the living conditions of many Americans.

Passing anything like this will be extremely difficult given the Democrats' razor-thin majorities in the US Congress.

Eventually, Mr Biden should be able to win the support of the House of Representatives, despite objections from several New York-area representatives who want to lift the cap on deductions for state and local taxes imposed by the Trump tax bill. The Senate, however, is an entirely different matter. And Democratic hopes of passing any such bill this year begin with a little-known official called the Senate "parliamentarian".

The pandemic bill, like Mr Trump's tax cut, was adopted by a simple majority under “budget reconciliation” – an unwieldy workaround to bypass the 100-member Senate's otherwise inflexible 60-vote supermajority to allow legislation to move forward. This exception to the filibuster only applies to spending proposals, meaning that all or most of the infrastructure legislation will probably, but not certainly, qualify.

The main complication is that reconciliation, being supposedly a budget procedure, has never been used twice in the same year. Whether it can will be ruled on by Elizabeth McDonough, the Senate’s professional parliamentarian who referees issues of parliamentary procedure and the correct application of Senate rules.

Ms McDonough has already shown herself willing to thwart the re-empowered Democrats by correctly ruling that a minimum wage increase that had been intended for the pandemic relief bill exceeded the parameters of what is allowed under reconciliation and therefore had to be removed.

A simple Senate majority can always overrule the parliamentarian, but that’s rare and arguably improper. Ms McDonough is a fair-minded arbiter, and changing the rules – not overruling her impartial interpretations – is the appropriate response to an unwelcome ruling.

If she finds that the infrastructure bill can move forward despite reconciliation already having been used for pandemic relief, the really difficult problems commence.

Unless Mr Biden can win some Republican support, which seems exceedingly unlikely on this or any other significant legislation, he will need to hold every single Democratic vote in the 50-50 split Senate, with Vice President Kamala Harris breaking the tie.

Some conservative Democratic senators from largely Republican-leaning states, especially Joe Manchin of West Virginia and Kyrsten Sinema of Arizona, will find supporting such an expansive spending programme politically risky. Moreover, for the same reason they strongly oppose filibuster reform – to preserve their own centrality in Senate deliberations under current circumstances – they may be tempted to either greatly dilute the proposed legislation or simply oppose it altogether.

Mr Biden's ambitions are at least as grand as those of Lyndon Johnson in the early 1960s. But he will have to somehow channel Johnson’s legendary parliamentary skills and powers of persuasion to prevail.

Prospects are even dimmer for another potentially historic bill, this one on securing voting rights, which would require reforming or bypassing the filibuster. That isn't necessary for the infrastructure spending package. But the same block of all 50 Democratic Senate votes plus Ms Harris' tiebreaker will probably be needed to secure either.

Yet the pandemic relief, infrastructure and voting rights acts – if all three passed – would almost certainly make Mr Biden a transformative president, probably beyond even Johnson's legacy and closer to Roosevelt's.

Such an achievement would be all the more remarkable because it can only be done by keeping the fractious and still ideologically diverse Democratic Party unanimously united behind extraordinarily bold spending plans. And in the unfortunate event any one of the several elderly Democratic senators passes away, his task would become even more daunting and perhaps impossible.

So his margin for error or bad luck is close to zero.

Yet Republicans lack a coherent rebuttal other than budget concerns. Since they evinced no interest in fiscal discipline during the Trump administration, that will be highly unconvincing for anyone paying attention to their stances. And a major infrastructure project would probably be broadly popular, including among Republican voters.

Such spending would generate huge numbers of good working-class jobs, which Mr Trump always promised but never really delivered beyond what the economy was already in the process of achieving. His endless but meaningless "infrastructure weeks" became a national joke.

If Mr Biden can hold the Democrats together, pass transformative legislation while defeating the pandemic, and avoid sustained, high inflation (the obvious danger of such huge expenditures), the Democrats would be in an extraordinarily strong position.

Typically, a new president's party loses congressional seats in the first midterm, and Mr Biden cannot afford any losses in either the House or the Senate next year. But the historic exceptions have always come during times of crisis, and no one doubts there is one now.

If Mr Biden shows that sweeping government actions can solve big problems, the existing Republican playbook may be rendered obsolete. They will finally have to abandon the Donald Trump personality cult and categorically opposing almost everything, and seriously reengage with policy and governance.

Hussein Ibish is a senior resident scholar at the Arab Gulf States ­Institute and a US affairs columnist for The National