Rep. Ken Buck (R-Colo.) on Thursday dealt one final blow to House Republican leadership one day before leaving Congress by signing Democrats' foreign aid discharge petition.

Why it matters: Buck is the first Republican to sign onto that discharge petition – or any Democratic discharge petition this Congress – amid GOP concerns about surrendering the House floor to Democrats.

Driving the news: The discharge petition, which would force a vote on the Senate's $95 billion aid package to Ukraine, Israel and Taiwan, is now up to 188 signatures with Buck, according to the House clerk's website.

• The measure needs 218 signatures to force a vote, however, and many progressives have said they won't sign onto it.
• Rep. Brian Fitzpatrick (R-Pa.) has a competing discharge petition on a $66 billion munitions-only aid package that also includes border security policy changes, which was introduced by a bipartisan group of centrists.
• That discharge petition has just 16 signatures, according to the clerk's website, and 10 are Republicans, most recently Buck.

What he's saying: Buck, whose resignation from Congress takes effect on Friday, told reporters "we've got to fund Ukraine and help people who are yearning for freedom."

• Buck said he talked both to Fitzpatrick and several Democrats about signing the petitions.
• Buck said he likes Fitzpatrick's discharge petition, in particular, because it "also covers the border."

Between the lines: A quirk in House rules allows Buck's signature to count towards 218 until his district votes in a special election to replace him.

• The special election is scheduled for June 25 and is likely to result in a conservative replacement disinclined to support either discharge petition.

Context: Buck has proven a persistent thorn in Republican leadership's side during this congressional session. He has vocally criticized efforts to impeach President Biden.

• On Tuesday night, the House Freedom Caucus — a right-wing group of which Buck has long been a member — voted to kick him out.

Go deeper: House Freedom Caucus kicks out another member