Under the US Constitution, an "actual enumeration" of everyone living in the United States must take place every decade. Seats in the House of Representatives are then apportioned according to "the whole number of persons in each state." The census also determines each state's quota of electoral college votes, as well helping shape electoral maps and ensuring the equitable allocation of some $900 billion in federal funds for Medicaid, development grants, public schools, law enforcement and disaster relief.

Despite the Census Act's requirement that Congress be notified of planned questions three years in advance, citizenship was not on the list sent to Congress by commerce secretary Wilbur Ross in March 2017. But we now know that the topic was being discussed within the White House, though perhaps mainly among since-departed right-wing functionaries like Steve Bannon and Stephen Miller.

The public debate was kicked off by a leaked January 2017 draft executive order calling for the Census Bureau to add the question as part of a range of new immigration enforcement measures. Secretary Ross approved the question in March last year, overriding career officials at the bureau who were concerned that the question would reduce the response rate among immigrants who have not yet become citizens. That fear has since been heightened by Trump's threats that immigration enforcement agents will begin rounding up and removing millions of illegal immigrants.

In congressional testimony Ross denied having discussed the matter with the White House and said he was responding solely to a request from the justice department, which claimed to need the information to enforce the Voting Rights Act. But it emerged that he had discussed the matter with Bannon and attorney-general Jeff Sessions in spring 2017. Leaked emails show the idea had been pushed by a political appointee who, in private practice, had defended partisan electoral boundaries introduced by Republican legislators.

Even without the citizenship question, testing of the existing 2020 census questionnaire has revealed a heightened reluctance to answer the survey, and increased concern about confidentiality and privacy. Although the federal government is barred from using individual census data for law enforcement, most people don't know or perhaps don't believe that.

For some states in particular, inaccurate census data will result in less representation in Congress and less federal funding. By one estimate, 6.5 million people will be missing nationally, with Arizona, California, Florida, Illinois, New York and Texas potentially losing seats in Congress.

Along with lawmakers in states like California and New York, urban leaders, who are mostly Democrats, are alarmed by the proposed question. Recent evidence suggests that the question was drafted specifically to benefit Republicans. In 2015, a party strategist, Thomas Hofeller, conducted a study that found a citizenship question would help Republicans in their efforts to shape electoral boundaries to their advantage during the periodic "redistricting" process.

Not surprisingly, more than 20 states, cities and civil liberty groups, filed lawsuits about this issue, culminating in a Supreme Court decision that shocked Trump and his administration. In what has been described as a "split the baby" decision, the Supreme Court upheld, 5-4, the decision of the New York District Court requiring the commerce department to give a true explanation for its decision to include the citizenship question in the census.

Chief justice John Roberts was the surprise swinging vote. He sided first with the conservatives on the court to uphold the right of the administration to add the question, finding that this was constitutionally and statutorily permissible. Then he switched sides and, with the four liberals on the court, held that the commerce secretary had not given the true reasons for needing the question on the census. In the opinion written by Roberts, it was suggested that Ross was motivated by partisan politics and could face charges for his "pretexts" (a lawyerly term for lies) and for blatantly misleading the courts.

The justice and commerce departments appeared to accept the Supreme Court decision, asserting that the courts would be heeded; Trump, fuming, had other ideas. At 1.04am on American Independence Day he undercut his officials to tweet that "News Reports about the Department of Commerce dropping its quest to put the Citizenship Question on the Census is incorrect or, to state it differently, FAKE! We are absolutely moving forward, as we must, because of the importance of the answer to this question."

Trump then said he was considering an executive order to force the question onto the census. In a round of chaotic manoeuvring, administration officials reversed themselves and pledged to restore the question to census forms. Attorney-general Barr now says the Supreme Court decision was wrong, and that there is "an opportunity potentially to cure the lack of clarity that was the problem" - presumably this means Wilbur Ross's lies - "and that we might as well take a look at doing that."

It's hard to imagine Chief Justice Roberts and House leader Nancy Pelosi allowing Trump to get away with this testing of the boundaries of executive power, and this is why some legal experts see a constitutional crisis looming. It certainly puts the White House squarely at loggerheads with those two bodies.

From a logistical point of view, any delay or add-on could be problematic. The census is mandated to take place on April 1, 2020 and changing the date would require an act of Congress. Printing and distributing a separate question would be prohibitively expensive.

Even if the troublesome question doesn't make it into the census, the damage has probably already been done, with people's confidence in the process compromised. The job of the thousands of census workers in certain neighbourhoods has been made doubly difficult. Beyond the census itself, this has now become a civil rights issue.

Unless there is a reasonable resolution soon, this contentious issue will be a major factor in the 2020 election. Trump's recent tweets give an indication of how he will use the census to play to his base. On Tuesday he tweeted about the "strained" Supreme Court ruling, saying it "shows how incredibly important our 2020 Election is."