By fooling the public. The press, academia, Congress, etc. are on the same wavelength, and "the lie" sounds so plausible that it is effective.
-- but he and his conservative purists shout Constitution every chance they get, yet ignore this. --
They are so invested in the outcome, that "magic thinking" ensues. Judges do this too.
-- Why is it not cleared up or really, why has he not left the race for the sake of the country? --
The fullness of time may reveal a surprise. The public would not be as aware of this issue, but for his "pushing it" by sticking to his position.
-- ... he should have cleared it up when he had the chance. Now we are voting. --
Secretaries of State don't care if the names on the ballot are eligible for office or not. There have been people taking office, and found ineligible. And at this point, the wasted votes only amount to a handful of convention delegates that the RNC can take from Cruz and give to Jeb, at the convention.
Not to say it isn't a big deal, but it's not as big a deal as Congress facilitating Obama's usurpation of the office, just as it would have facilitated McCain's usurpation.
So what you are saying is there is almost no way he is a Natural Born Citizen.
Do we know if his father was a US Citizen when Ted was born or had he become a Canadian citizen?