Why do Kevin McCarthy's Republicans want to impeach Joe Biden now?

Speaker of the House Kevin McCarthy has announced a formal impeachment inquiry into President Joe Biden.

After weeks of hints and veiled suggestions, the California Republican took the plunge in a brief statement to the press that there were "serious and credible allegations into President Biden's conduct" that "taken together" necessitated further investigation.

Impeachment by the House of Representatives is the first step in a formal process to remove a president - or other senior executive or judicial official - from office. It requires a simple majority vote in the chamber to trigger a trial in the US Senate, where a two-thirds majority is necessary for conviction and removal.

President Donald Trump was impeached twice when Democrats controlled the House - over Ukraine in 2019 and the January 6 Capitol riot in 2021 - but was acquitted by the Senate on both occasions.