The slow pace of admitting Syrian refugees into the country has prompted 27 Democratic senators to voice their concerns in a letter to President Barack Obama.

The White House has said it intends to admit 10,000 Syrians for resettlement by Oct. 1, but so far, slightly over 1,700 have been admitted.

“There is no denying there’s work to do,” White House Press Secretary Josh Earnest said on Friday.

Related: [White House Hedges on Syrian Refugees]

Earnest said that progress so far, numerically, has been “linear.”