A little late, but here is an analysis of the votes for the KeystoneXL pipeline vote in both houses of Congress. DW-NOMINATE, shown in the linked graph, is the standard way of measuring ideology in modern studies of the United States Congress. The Y-axis used to measure views on race, and now maybe taps region (but we don’t know). The X-axis is the main ideological axis. Negative numbers mean more liberal and positive numbers mean more conservative (usually the values are capped at -1, +1). As their post points out, their model accurately predicts that moderate democrats would oppose the legislation (and which is what we largely saw).

The bigger point, at least to me, is that there is no reason to protect the President with respect to this issue and Democrats didn’t protect him. The Senate needs 67 votes to override a veto and and 290 are required in the House. S.1, the KeystoneXL construction bill, got 62 and 270 respectively. This means that five votes are required in the Senate and 20 in the House (In the Senate, Sen. Rubio (R-FL) was absent from the original vote so the number in the Senate is actually 4).

Looking at the Senate roll call vote, it is very unlikely that any of the no votes would flip to override the President considering they are all Democrats or caucus with the Democrats. That situation is the same in the House with the vote probably having as many Democrats on the Aye side that it’ll get and with most of the non votes being Democratic.

This is all to say that Members of Congress were able to vote whatever position they thought would serve them best — which is what we saw — because there wasn’t anything at stake policy wise. Several Democrats voted to build the pipeline because it served their electoral incentives. At the same time, those who voted for the pipeline were able to do so knowing that the policy had little chance of becoming law and that the President was willing to veto the bill. It doesn’t particularly matter if they supported the policy or not (though some probably did). Rationally, if there was any chance of voting against building the pipeline would hurt you (as an MC) then you could fairly easy just vote for it and largely neutralize the issue. This would also probably help members in swing districts because they could also say they distanced themselves from the President.

Long story short, the President protected conservative Democrats with his veto because they were able to vote how they wanted with no real ramifications.