Not in the US, no. There is no "taking over" by a VP unless the president is incapacitated. Every 4yrs there's a presidential election. The 2020 Democratic nominee must be able to be the 2024 incumbent. The history of one-term presidencies is not good.
The last one-term presidency was Carter. The only Democrat between 1968 and 1992. One-term presidencies are damaging to that party. If Biden were to be the nominee, the opposition will just wait out his 4yrs. He is frail now. In 2024 he will be 83. These are real concerns.
The last one-term presidency in an open election was Carter--the last one-term presidency with a VP was Bush 1: Reagan's 3rd term, as VPs are called. So in a one-term presidency the VP would be carrying the weight of that failure. AND would have Dem challengers like Gore did.
So if Biden were the nominee, his VP would be running with his baggage but fighting off both Democratic and Republican challengers. So this idea that a Biden VP just takes the presidency is historically dead wrong.
