The tribulation Jesus was speaking of in Matt 24 clearly happened already. He is fore telling the destruction of the temple and of Jerusalem, he is telling the disciples of the spreading of the gospel to the whole world, a fulfillment of the Great Commission.
Clearly it is the elect that the tribulation comes upon. Who is it that you take the elect to be meaning in the Discourse?
Matthew 24:21 For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.
Mark 13:19 For in those days shall be affliction, such as was not from the beginning of the creation which God created unto this time, neither shall be.
20 And except that the Lord had shortened those days, no flesh should be saved:
but for the elect's sake, whom he hath chosen,
he hath shortened the days.
Matthew 24:23 Then if any man shall say unto you, Lo, here is Christ, or there; believe it not.
24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
Mark 13:26 And then shall they see the Son of man coming in the clouds with great power and glory.
27 And then shall he send his angels,
and shall gather together his elect from the four winds,
from the uttermost part of the earth to the uttermost part of heaven.
It seems pretty clear from these passages that the elect can only be meaning the church.