I understand your question deals with 'American Christians' and that's being well discussed!
But to see the differences in Jesus' mission or reception, wouldn't we have to examine how Jesus would be received in a
Theocracy though (as Judea was, with an overlay of Imperial Rome) not in a "Western secular" society?
Jesus was making his points by referring to pre-existing Sacred Scriptures ... and his Life and the "religion" that arose from his life and Teachings was based upon his fulfilment of culturally
accepted Sacred Prophecies. (even amongst the pagans who became Christians, much was made of the claim that Jesus had been PROPHESIED and then ACTUALLY ARRIVED etc)
To have the same or
comparable impact as Jesus had then, his teachings would have to be based upon the "fulfillment" of expected Prophecy (which only exist NOW among "American Christians" as being his SECOND COMING.)
In a science-influenced culture such as America is today (where even
Christians are heavily influenced by Science and Technology -- don't delude ourselves on that) ... Jesus might have to be seen as fulfilling SCIENTIFIC expectations, rather than theocratic or Scriptural ones (of ancient Palestine) -- he'd have to be amazing us via "scientific miracles" and re-illuminating scientific dogma for an amazed crowd (rather than dealing in already-fulfilled Scripture or religious "miracles")
Imagine if EINSTEIN's theories and thoughts -- in his revolutionary re-imaging reality -- had a definite RELIGIOUS SUPPORT.
If E=MC2 were a religious statement, by the long-awaited prophecised messiah.
weirdness and hijinx would ensue
I respect the question, but have to consider the tangent here. "American Christians" and JESUS?
You pose a question in which -- if he's JESUS -- they'd know him.
If the question becomes "if a guy shows up saying the same words as Jesus said, but his words
aren't linked to Jesus' own words, in the minds of American Christians ..." then
that's the issue. Otherwise, you're saying he'd just be preaching a return to JESUS' WORDS.
Fundamentalists are doin' awright, these days.
This "different" Jesus would still be peeing off the religious hypocrites of ancient and modern days, sure.
But the STATE wouldn't be torturing and executing him. The religious Establishment wouldn't have that authority either.
What if BUDDHA came back to INDIA ???
There aren't many Buddhists left in the homesoil of Buddhism, relatively speaking ... buddhism went throughout asia and sort of fell into disuse in India (though I think Buddha was born in what is now NEPAL?)
What if MOHAMMAD came back to Saudi?
And preached some of his messages about all the "Children of the Book" co-existing in religious TOLERANCE. (Remember, the battles Mohammad fought with Jews THEN were basically secular wars between Jewish towns over TRADING and TAXES ... not religious war) heck, originally mohammad wanted muslims to pray towards JERUSALEM, not MECCA, I've heard.
What if NEWTON showed up in London? 
He'd be all ... "quantum WHAT?" ... but then he'd be "But I see you still haven't figured out GRAVITY have you? So hah!"
'It's a Universe of crystal spheres. It's elephants all the way down after that!'
