Are normal backdoor Roth IRA and mega backdoor Roth IRA still possible in 2018 tax plan? I had troubles figuring it out due to number of different plans.
The new tax law has no impact on either the backdoor Roth IRA or the mega backdoor Roth. Tough to find a definitive source on something that didn't change, but here's a post from Mad Fientist confirming this.
As mentioned in that link though, the new tax law did remove the ability to recharacterize Roth conversions. So if you do a backdoor Roth and your income ends up being much lower than expected, you can't undo the conversion and take the Traditional IRA deduction instead.
The House Conference Report for the Tax Cuts and Jobs Acts has footnotes in it that explicitly permit the back door Roth:
Although an individual with AGI exceeding certain limits is not permitted to make a contribution directly to a Roth IRA, the individual can make a contribution to a traditional IRA and convert the traditional IRA to a Roth IRA.