There could be various factors that affect the way votes are cast in any presidential election, including public opinion, the political climate at the time, and logistical considerations like mail-in voting availability. However, it’s important to note that specific predictions like ‘one in 6 presidential votes will likely be cast by mail for Harris’ involves a level of speculation that can’t be accurately made. You would need specific credible polling data or studies to support this claim.
Moreover, assuming this statement is meant for the current Vice President Kamala Harris, she isn’t running as a presidential candidate at this moment. Thus, stating that one-sixth of the votes will be cast for her specifically might not be accurate.
Lastly, mail-in voting can fluctuate heavily depending on the situation around election time. For example, during the COVID-19 pandemic, mail-in voting was more popular due to social distancing measures. It might not be the case in non-pandemic times.
To get an accurate sense of mail-in voting trends or predictions for a specific candidate, I would advise checking the latest credible polls or election studies.