There are a number of Democratic candidates for President and each of them have different ideas on what to do with the Medicare program. Some of the Democrat's Medicare proposals are explained in more details.
Many Democratic presidential candidates are campaigning on changing the healthcare system that we know today to Medicare For All. Some candidates want to keep Medicare as it is now but expand it as an option to the rest of the population. Other candidates want to have Medicare be the single payer of healthcare and eliminate private insurance carriers. What will ultimately be seen greatly depends on who's elected and how negotiations pan out.
Many of the 2020 presidential candidates will be discussing Medicare for the campaigns. President Trump has repeatedly said he would not touch Medicare, but has cut budget funding to Medicare for 2020 with hopes of making the money back by reducing spending. There is no public plan available about Trump's Medicare stance going forward though that may be subject to change as healthcare will be a big talking point.