It has been widely reported that the Tax Cuts and Jobs Act eliminated the ability to recharacterize Roth IRA conversions as of January 1, 2018. On the other hand, it kept the ability to recharacterize IRA and Roth IRA contributions. Despite all the above, an unanswered question on Roth IRA conversions done in 2017 lingered. At the time of those conversions the taxpayer had the ability to recharacterize the conversion up to October 15, 2018. Was that option still available to them?
On January 18, 2018, IRS updated its FAQ pages to say that 2017 Roth IRA conversions could be recharacterized up to October 15, 2018. Following is the text from the IRS website:
How does the effective date apply to a Roth IRA conversion made in 2017? 
A Roth IRA conversion made in 2017 may be recharacterized as a contribution to a traditional IRA if the recharacterization is made by October 15, 2018. A Roth IRA conversion made on or after January 1, 2018, cannot be recharacterized. For details, see “Recharacterizations” in Publication 590-A, Contributions to Individual Retirement Arrangements (IRAs). Here is a link to the updated web page:https://www.irs.gov/retirement-plans/ira-faqs-recharacterization-of-ira-contributions
This is good news for taxpayers who did not have the time to recharacterize before year end, especially considering the small amount of time they had to get a recharacterization done.  But all taxpayers considering a Roth conversion in the future will need to plan far more carefully for their conversion. There will be no second chances; no way to get out of paying the income tax due on the conversion. It is likely that there will be fewer Roth IRA conversions and smaller conversions in the future.
https://www.irahelp.com/slottreport/roth-recharacterization-update-irs