Pub 17, page 196 (2018):

Gambling Losses up to the
Amount of Gambling Winnings
You must report the full amount of your gambling
winnings for the year on Schedule 1 (Form
1040), line 21. You deduct your gambling losses
for the year on Schedule A (Form 1040),
line 16. You can't deduct gambling losses that
are more than your winnings.
You can't reduce your gambling winnings
by your gambling losses and report
the difference. You must report the
full amount of your winnings as income and
claim your losses (up to the amount of winnings)
as an itemized deduction. Therefore,
your records should show your winnings separately
from your losses.

However, from The Taxbook (2018):

Court Case: A taxpayer won $2,000 on a slot machine, but ended up ahead only $1,100 at the end of the day. The taxpayer did not report the winnings on the tax return, and did not itemize deductions to claim the losses. The IRS claimed the taxpayer failed to report gambling winnings of $2,000. However, Tax Court determined the amount of unreported gambling winnings was $1,100. The decision stated that computing wins and losses for each separate wager was too burdensome, and “the fluctuating wins and losses left in play are not accessions to wealth until the taxpayer redeems his or her tokens and can definitively calculate the amount above or below basis (the wager) realized.” (Shollenberger v. Commissioner, T.C. Memo 2009-306)

So who knows?