A 2012 study by The Pew Charitable Trusts estimates that 24% of the voting-eligible population in the United States are not registered to vote, a percentage that represents "at least 51 million eligible U.S. citizens."
Democratic political data firm TargetSmart collected registration data from states and reported to POLITICO that the number of registered voters hit a new record ahead of the general election topping 200 million people — 2S00,081,377
Surveys conducted in 2017, 37% or 74 million of registered voters identified as independents, 66 million as Democrats and 26% or 52 million as Republicans, another 51 million not evern registered to vote.Mar 20, 2018
If half of the eligible voter who is not currently registered would register with the Constituion Party along with half of the voters that are registered with no party affiliation, the Constsitution Party would have a membership of over 63 million which would make it large significantly larger than either the republican or democratic parties.