Harley's declining domestic sales in 2019 of about 5.2%, only reflect the general overall market trend of declining US sales. US Motorcycles sales for all marques declined by about 3.1% in the US in 2019. This has been a steady decline since 2007 when a peak volume of around 1 million units were sold. In 2019, less than half that, at around 472,000 units total. Harley's piece of the pie was about 126,000 units.
Harley sales also declined globally, but by a smaller percentage. International Harley sales declined 3%, to around 92,300 units. Harley has the biggest chunk of the USA domestic market, and sells substantial numbers of machines internationally. They are not out of the game by any means.
It's interesting to compare the US market to the world largest motorcycle marketplace; India. Although the India motorcycle market grew in 2019, the player that occupies the premium priced segment in that market, Royal Enfield, saw a substantial decline in sales volume. Even at that, they still made a lot more bikes than Harley does.
USA 2013 | total units 465,800 | Harley Davidson 167,000
India 2013 | total units 14,300,000 | Royal Enfield 178,100
USA 2019 | total units 472,000 | Harley Davidson 126,000
India 2019 | total units 21,180,000 | Royal Enfield 690,840