Looking at the 2018 election Van Drew representing the DP won in a district voting heavily for Trump in 2016. He was always going o be in trouble in 2020 and now had a meeting with Trump in the issue of switching from the DP to the RP and I believe the final decision will depend on whether the RP will be prepared to nominate him as their candidate in the area he at present represents.
The chances are that the RP may agree to it as happened in the past. If that is agreed upon and bearing in mind the leftist approach of the DP at present - how many of the Democrats representing districts where Trump won in 2016 will also switch parties. There are already another 5 DP members not going to vote for impeachment and that will set loose the socialist tigers in the party, making it virtually impossible for the relevant members to be re-nominated as DP candidates,
The figures will become clearer when the House actually vote for impeachment this week. It is quite likely that DP members voting against impeachment will likely be looking for a new political home before 2020 - since the socialists in he DP would fight them all-out not to re-nominate as candidates in 2020 and they have no political future in the DP. They may be more successful standing for the RP in future.