WASHINGTON—Support grew among Democrats for impeaching President Trump over the Capitol riot and a new Republican senator indicated openness to such a step, while the president remained out of public view and authorities charged more rioters.

An expanding number of House Democrats had signed onto an article of impeachment by Saturday that a trio of House Democrats plan to introduce on Monday. Their single article of impeachment focuses on Wednesday’s violent breach of the Capitol complex and accuses the president of inciting an insurrection.

One of its authors, Rep. David Cicilline (D., R.I.), said Saturday on CNN that they now have 185 Democratic supporters and hope to get some Republicans as well, up from more than 150 on Friday as fallout from the deadly riot at the Capitol continued.