...The tribulation... is for the unbelievers...
Note that we Christians are referred to throughout Revelation (6:11, 7:14, 9:4, 12:17, 13:7-10, 14:12-13, 15:2, 16:15, 18:4, 20:4), and there are no Christians outside of the church (Ephesians 4:4-5).
...His wrath will be poured out...
Note that we can be in the tribulation without being appointed to God's wrath, for during the tribulation nobody in heaven says God's wrath "is come" until near the end of the tribulation, after the 7th trumpet (Revelation 11:15, 18), in the 7 vials of God's wrath (Revelation 15:1; Revelation 16), and none of the 7 vials are poured out on those of us who have obtained salvation; I believe we are even blessed at the 6th vial (Revelation 16:15), that we might endure to the 1,335th day after the abomination of desolation (Daniel 12:11-12), which is the day I believe Jesus will come back (Revelation 19).
I think it's important to make this distinction because many people -- including many Christians -- are going to be blaming God for everything bad that happens to them in the tribulation; they're going to be saying that God is the one causing all of their suffering, when in reality it will be Satan, evil men, and natural disasters that are causing it.
Satan is going to try to use the suffering of the tribulation to turn people -- even us Christians -- away from God, to get us to believe that God is really a cruel and unjust tyrant who only wants mankind to suffer and be tortured, while Satan is the one trying to help us. We need to be able to say, no, this suffering is not from God, but from evil and natural sources, just as we Christians have always had to suffer in wars, famines, plagues, persecutions, and natural disasters throughout history, from the beginning of the church down until this day.
In the pre-trib view, will those who "obtain salvation" in the tribulation be "appointed to wrath?" Aren't being "appointed to wrath" and "obtaining salvation" mutually exclusive?
"God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ" (1 Thessalonians 5:9).
...The terrible day of the Lord, as it is called in Joel, IS the tribulation....
Is there a verse that says or requires that the day of the Lord begin before the 2nd coming?
I believe the day of the Lord will begin at the 2nd coming, and is the day we wait for (1 Corinthians 1:7-8), watch for (1 Thessalonians 5:2-6), and will rejoice in (2 Corinthians 1:14).
"Waiting for the coming of our Lord Jesus Christ: Who shall also confirm you unto the end, that ye may be blameless in the day of our Lord" (1 Corinthians 1:7-8).
"Yourselves know perfectly that the day of the Lord so cometh as a thief in the night... But ye, brethren, are not in darkness, that that day should overtake you as a thief... let us not sleep, as do others; but let us watch" (1 Thessalonians 5:2, 4, 6).
"We are your rejoicing, even as ye also are ours in the day of the Lord" (2 Corinthians 1:14).
Paul said the day of the Lord will come as a thief in the night (1 Thessalonians 5:2) and the Lord said he will come as a thief (Matthew 24:43-44), and there's no 3rd coming of the Lord.
I believe the subject of 2 Peter 3:4-10 is the promise of the Lord's 2nd coming: "Where is the promise of his coming?... The Lord is not slack concerning his promise... the day of the Lord will come as a thief in the night" (2 Peter 3:4, 9, 10).