This has been going on for awhile now and seems to be picking up steam as Election Day gets closer:

https://twitter.com/THEnxtxrixusTIG/status/256578519319068672

https://twitter.com/E_Zz_E/status/256618439299440642

https://twitter.com/Sm0keGudFucKGud/status/255860955261595649

https://twitter.com/Tweet_thenLaugh/status/256859318828294144

https://twitter.com/doonyelkriaf/status/256608928182452224

https://twitter.com/xSincerlyYours_/status/256577291864383490

https://twitter.com/RealDopey/status/256206187475922944

Others encouraged the assassination of Romney:

If ROMNEY Win I hope somebody KILL HIM . — MunecaFace (@_MunecaFace) October 12, 2012

https://twitter.com/Shonni_OFWGKTA/status/256838262981816320

https://twitter.com/MariahMimi_/status/256880786911932416