Note that “toss-up” races are races where the general election (i.e. between the Democratic and Republican candidates) is a toss-up. By guess is that in such races, an extra $2,500 spent on TV ads is necessary to net a candidate one extra vote. This is because the pool of persuadable voters is much smaller: most voters will vote for the Democrat no matter what or vote for the Republican no matter what. By contrast, spending goes a lot further in primary elections.
Note that “toss-up” races are races where the general election (i.e. between the Democratic and Republican candidates) is a toss-up. By guess is that in such races, an extra $2,500 spent on TV ads is necessary to net a candidate one extra vote. This is because the pool of persuadable voters is much smaller: most voters will vote for the Democrat no matter what or vote for the Republican no matter what. By contrast, spending goes a lot further in primary elections.