Dave Weigel of Bloomberg Politics tweeted a funny story Wednesday in which Sen. Lindsey Graham of South Carolina called Arizona’s Sen. Jeff Flake the “RINO of the year.” (That’s Republican in Name Only.) Indeed, Flake has taken some centrist positions; he was against the 2013 government shutdown and suing President Obama for his executive action on immigration.

If you had tried to tag Flake with the RINO label two years ago, however, I would have been very dubious. Flake, then in the House, was considered one of the most conservative candidates for the Senate in 2012. According to DW-Nominate scores, which look at a member of Congress’s roll call votes, he was in the 98th percentile for conservatism among House Republicans in his final year in the chamber. He was endorsed for the Senate by Jim DeMint’s Senate Conservatives Fund.

But Flake’s election to the Senate changed him. He became a senator in a state in which more Democrats than Republicans were elected to House in 2012. With a more moderate constituency, Flake became more moderate. And Flake isn’t alone in his change of heart.

Since Obama became president, five members or former members of the House, including Flake, became senators from states that Obama won twice or in which a majority of the House delegation was Democratic after 2012. That is, states that could be described as blue or purple.

In all five cases, the senators were more moderate relative to Senate Republicans than they were to House Republicans.

Sen. Dean Heller of Nevada was in the 80th percentile for conservatism among House Republicans in the 112th Congress but in the 30th percentile for conservatism among Senate Republicans in the 113th Congress.

Sen. Mark Kirk from the blue state of Illinois was in the 52nd percentile for conservatism among House Republicans in the 111th Congress but in the seventh percentile for conservatism among Senate Republicans in the 113th Congress.

Sen. Rob Portman of Ohio was in the 48th percentile for conservatism among House Republicans in the 109th Congress, but he dropped to the 38th percentile for conservatism among Senate Republicans in the 113th Congress.

Sen. Pat Toomey of Pennsylvania was in the 94th percentile for conservatism among House Republicans in the 108th Congress, but he dropped to the 57th percentile for conservatism among Senate Republicans in the 113th congress.

What’s amazing about these transformations is that the Senate has generally been found to be the more moderate of the two bodies. If conservative members of the House were joining the Senate and staying ideologically consistent, we’d expect their conservatism relative to the rest of the body they were in to go up. The opposite has happened.

These senators are changing their voting records to become closer to the center of electorate in their given states. In doing so, they’re setting themselves up to have an easier time in their re-election campaigns.