I periodically write down notes for what I want to include in my platform for election reform and related issues, and the census issue is one of those items. Some people have disputed what Elon says but he's correct.

From census.gov, regarding apportionment in Congress:
The apportionment population count for each of the 50 states includes the state’s total resident population plus a count of the overseas federal employees (and their dependents living with them overseas) who have that state listed as their home state in their employers’ administrative records.

The resident population counts include all people (citizens and noncitizens) who are living in the United States at the time of the census. People are counted at their usual residence, which is the place where they live and sleep most of the time.

Article 1, Section 2, of the United States Constitution states:

"Representatives and direct Taxes shall be apportioned among the several States which may be included within this Union, according to their respective Numbers...The actual Enumeration shall be made within three Years after the first Meeting of the Congress of the United States, and within every subsequent Term of ten Years, in such Manner as they shall by Law direct."

It makes no sense, and I believe it's unconstitutional, to suggest representation / apportionment is based on people that are not US citizens.

The People established this nation for themselves and at no time during our founding did they just lump in others, and in fact they put in language talking about naturalization of non-citizens. If representation was to be based on citizen and non-citizen numbers, there would be no need to even discuss citizenship or naturalization. The core element to our founding was the establishment of a representative form of government, a constitutional republic to protect the individual rights of CITIZENS while allowing those CITIZENS to steer the direction of their respective states and the states to help steer the nation, via federalism. Citizenship is fundamental to all of this.

We are a union of states, each state composed of citizens, and citizenship meant so much that, even though most people were subjects of the Crown at the time of our founding, they did not transfer that status to this new place, making us British citizens of the United States territories or something like that.

There's a reason our Founders consulted the historical lessons of other nations so often when they wrote the Constitution and debated its ratification via the Federalist Papers etc - our nation was going to be unique, and sovereign, built by its own citizens, for the betterment of its own citizens - a distinct group of people. Citizenship, belonging, the status of being "American" was so special for the Founders and Colonists that they bound themselves together to cast off a tyrannical regime and instituted a new government and a new nation in order to protect all that they believed was entitled to a citizen. They went to war for this.

Citizenship is substantive and meaningful. It's not trivial. It's not a mere administrative designation having no consequence or uniqueness. It is the most cherished aspect of being an American - you are a citizen of this nation, bonded to every other citizen in a nation that our ancestors created - FOR US.

All men are created equal - and that means they have the ability to build their own nation, as our ancestors built for us. That equal nature does not give permission to invade our nation, violate our sovereignty, and then get the rewards of our citizenship or even the benefits of residence within this nation. To make that the case is to subjugate us to the non-citizen, which is to say that we are suddenly not equal, but inferior. When politicians argue for sanctuary, special treatment, and handing over the benefits of residence, citizenship, and the transfer from citizens to non-citizens, they are declaring that you, the citizen, are inferior to the non-citizen. It's an overt rejection of our Constitution and the entire platform on which our nation was founded. It is profoundly un-American, anti-American, and shows contempt for the People of this nation. It's not possible for anyone that espouses this position to have any legitimacy in government.

It befuddles the mind how anyone could interpret this differently.

There's no way to read the Declaration of Independence and not understand the central importance of citizenship:

The unanimous Declaration of the thirteen united States of America, When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.

We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security.--Such has been the patient sufferance of these Colonies; and such is now the necessity which constrains them to alter their former Systems of Government...