My research, as you term it, verified that not all citizens at birth are natural born, nor even native born. Some are, for Constitutional purposes, naturalized at birth. This is sometimes referred to as "acquiring" citizenship at birth, but only to distinguish it from individual naturalization of persons originally holding foreign citizenship. But since Congress has no power over citizenship other than via establishment of a uniform rule of Naturalization, anyone who "acquires" citizenship via a statute, must be considered "naturalized" for Constitutional purposes.
Charles Curtis was born in the US, was he not? Of parents who were citizens?
McCain would have qualified because he was born of two citizen parents, and "in the armies of the nation". Parents who have children while serving outside the country are deemed not to have left it's jurisdiction, and those children are deemed "born in the country". See Vattel, Book I, section 217.
Nor would the US Supreme Court have rejected all Obama eligibility challenges from being heard if there were constitutional grounds to disqualify him.
None were rejected on Constitutional grounds. The lower court cases were rejected on "standing" and "justicibility" grounds, while the Supreme Court never gives a reason for not hearing cases, so you can't make any conclusions from their doing so, nor does it create any precedent.
As to the Republican Party and the McCain Campaign, they were likely afraid of being termed "racist".
Sarah Pallin states in her book that she wanted to go into Obama's background, associations and so forth (but not specifically eligibility) but the McCain campaign would not let her. If they wouldn' let her talk about Bill Ayers or Rev. Wright, they sure as heck weren't going to even look at the eligibility of the first Black (well half Black) major party candidate for President. Wouldn't have been politically correct.
What’s stopping Sarah Palin from filing an amicus brief in support of any of the Obama eligibility lawsuits since November 5, 2008 and no more McCain campaign?
All you are good for is making excuses.
Why is Allan Keyes the ONLY marginally nationally known conservative to enter any lawsuit challenging Obama’s eligibility?
Why have none of the big, well-known conservative law firms such as the Center for Individual Rights supported any of the scores of eligibility lawsuits that have been filed?
The following major law firms all submitted amicus briefs in support of the partial birth abortion ban but none have submitted amicus briefs in support of any Obama eligibility lawsuit: Debevoise & Plimpton, O’Melveny & Myers, Morrison & Foerster, and Paul, Weiss, Rifkind, Wharton & Garrison.