If I failed to take the full RMD for 2019, am I able to take a distribution in 2020 and apply it to 2019?

[DawnC · Accepted solution]

Not unless this is your very 1st required minimum distribution (RMD).  

You must take your first required minimum distribution for the year in which you turn age 72 (70 ½ if you reach 70 ½ before January 1, 2020). However, the first payment can be delayed until April 1 of 2020 if you turned 70½ in 2019. 

If an account owner fails to withdraw an RMD, fails to withdraw the full amount of the RMD, or fails to withdraw the RMD by the applicable deadline, the amount not withdrawn is taxed at 50%. The account owner should file Form 5329, Additional Taxes on Qualified Plans (Including IRAs) and Other Tax-Favored Accounts, with his or her federal tax return for the year in which the full amount of the RMD was not taken. 

The penalty may be waived if the account owner establishes that the shortfall in distributions was due to reasonable error and that reasonable steps are being taken to remedy the shortfall. In order to qualify for this relief, you must file Form 5329 and attach a letter of explanation. See the instructions to Form 5329.

[dmertz]

Any regular distribution taken in 2020, including an RMD for 2019, will be taxable on your 2020 tax return.  If 2019 was not your first RMD year you'll want to file 2019 Form 5329 with your 2019 tax return to request waiver of the 50% excess accumulation penalty as DawnC indicated.