In the US, we take a population census very ten years and the next is in 2020. Regretfully, it seems the republicans are taking a thinly veiled attack at minorities by inserting an unnecessary question in the census. They ask if you are a citizen. This can cause countless millions to fail to report, which will be damaging for Democrats over the next ten years, which is their objective.
Frankly, it doesn’t matter whether you are a citizen or not for the census. The question has no impact on public services like roads, hospitals, shcools, police departments, emergency responders. Where it really causes problems is in mixed status households, of which there are about 9 million, where some members of the household are citizens and some are not. They, and millions of others, fear they may be deported.
Should you answer and answer truthfully or should you simply leave it blank? The law says you must answer truthfully. If you answer falsely, the potential fine can be up to $500. If you leave it blank, the fine is only up to $100. This article and this one, both from CNN with videos, tell you more about it.