snip ...

To a first approximation, Democrats should first shore up their own seats, then go after the low-hanging fruit next, meaning the Republican-held districts with a PVI of D+x, then EVEN, then R+1, then R+2, etc. The table below lists all 218 Republican-held seats by PVI. The second column gives the number of districts at each PVI. For example, there are four Republican-held districts that are R+1 and 11 at R+5. The last column gives the cumulative number of flips assuming they fall in order. So, for example, if the Democrats win all the Republican-held seats from D+3 to R+5, they flip 39 seats.