Draw a line between 2 zip code on US map in R

I have been trying to draw a straight line connecting 2 zip code in the US. So far I've only been able to plot points of each zip code in the US, but can't draw the line between them

Here is what my data look like. I am trying to draw 8 points on the US map and connect them, with 4 lines. I tried using zip.plot but it would only point points, not drawing a line

df1 <- data.frame(trip = c(1,2,3,4), zip1 = c(55803,87112,55107,66006), zip2=c(12909,93703,12205,78210))

df1
  trip  zip1  zip2
1    1 55803 12909
2    2 87112 93703
3    3 55107 12205
4    4 66006 78210