Everything to know about out-of-state donation flows
What a flow is. One arc per ordered pair of states: donors whose address is in the first state giving to the campaigns of House and Senate candidates whose seat is in the second. Only interstate money is drawn — a Texan giving to a Texas race is not a flow. Contributions are itemized individual gifts in the 2026 FEC bulk files, each counted once: conduit legs (ActBlue, WinRed) are dropped, and so are memo lines, which re-describe money already reported (a gift moved to the general election, or split with a spouse). Only money given straight to a candidate's own campaign committee counts. Joint fundraising committees are left out because they split their take among several recipients in shares these files don't show; party committees and leadership PACs are left out because they spend across many races. Giving above the legal limit is dropped: anything over $14,000 from one donor to one candidate, the most a person can give across a primary, a general and their runoffs.
Versus the national pattern. Take the share of Montana's out-of-state giving that goes to Texas, and divide it by Texas's share of the national out-of-state pool. Above 1× is an over-index, below 1× an under-index. "National" has to leave the states in question out: Texans can't give to Texas as an out-of-state flow, so Texas's share is measured against everyone else's money. Raw totals mostly rank the biggest states; the index takes size out, which is why the map uses it.
By party. With a party selected, the pattern is that party's own: Democratic money in Montana is compared with where Democratic money goes nationally.
Small pairs. When only a few donors would normally give between two states, the index can be influenced by a small number of donations. As a result each ratio is pulled back toward 1× based on how many donors are behind it. Pairs with a lot of donors barely change, but pairs with few donors are adjusted back toward 1.
Neighbors. A pair counts as neighbors if the two states share a land border or a metro area that crosses a state line (Kansas City, the DC suburbs, Boston–southern NH, Memphis, and so on). Those flows over-index heavily for reasons that are about geography rather than politics. The Hide neighboring states button at the top applies to everything on the page: arcs, every list, every total and every share. While they are hidden, the national pattern is refitted without them too, the same way a state's own cell is left out. Otherwise a state whose money mostly goes next door (New Hampshire to Massachusetts, Kansas to Missouri's Kansas City) would read as under-giving to every other state at once.