Representative Marie Gluesenkamp Perez, Democrat of Washington, was sitting through an Appropriations Committee meeting on Tuesday, staring up at the oil paintings of the past chairs of the powerful panel.

One, in particular, she found deeply unsettling.

“It’s concerning to sit there under a large portrait of Kay Granger,” Ms. Perez said, referring to the former Republican congresswoman from Texas who had suffered from mental decline for years when a conservative news outlet in her state found her, at the age of 81, living in an assisted living facility that included a memory care unit while she still held office.

The portrait served as a glaring reminder to Ms. Perez, the 37-year-old auto shop owner and second-term congresswoman who co-chairs the center-leaning Blue Dog Coalition, that she has served in Congress alongside aging colleagues, some of whom suffer from mental decline that renders them unable to perform large portions of their jobs.

Ms. Perez was hesitant to name any particular colleague, because she said the problem was bigger than any one person. But she said she was “concerned” about what she had heard about Representative Eleanor Holmes Norton, 88, the nonvoting delegate representing Washington, D.C., who is clinging to her seat despite clear signs of mental decline. There are other cases, she said, that are too painful to ignore.

So last month, Ms. Perez offered an amendment to a federal spending bill that aimed to create basic guidelines in Congress to ensure that members were able to do their jobs “unimpeded by significant irreversible cognitive impairment.”

Her amendment was unanimously rejected, which Ms. Perez chalked up to the fact that it prompted an “uncomfortable conversation” and that Congress does not like to make new rules for itself.