The Democratic Senatorial Campaign Committee (DSCC) is spending money on Sen. Arlen Specter's (D-Pa.) increasingly difficult primary.

As poll numbers show Rep. Joe Sestak (D-Pa.) catching up to the senator, a source confirms the DSCC is spending coordinated funds for Specter. The spending was first reported by my former colleague, Reid Wilson.

Coordinated funds differ from most party spending in that the committee can use the money to work with the candidate and supplement his or her ad buys. But such funds are capped at a certain amount depending on the race — $855,400 in the Pennsylvania Senate race — while non-coordinated or independent expenditure funds can be spent in unlimited amounts.

The DSCC has openly backed Specter over Sestak, but actually spending money on the race is a more unusual step. Specter is also getting an assist from President Barack ObamaBarack ObamaInauguration singer to Trump: Meet with me and my transgender sister NY attorney general: Transgender students to be protected despite withdrawal of Obama regulations Tillerson buys .6M home blocks from Obamas, Ivanka Trump: report MORE, who has cut a radio ad for him.

The committee spending has already led the National Republican Senatorial Committee (NRSC) to ask whether the DSCC will do something similar for Sens. Michael BennetMichael BennetA guide to the committees: Senate Senate advances Trump's Commerce pick Senate Dems move to nix Trump's deportation order MORE (D-Colo.) and Blanche Lincoln (D-Ark.), who both face primaries as well.