A federal judge in Boston on Tuesday temporarily blocked the U.S. Postal Service nationwide from implementing part of President Trump's executive order for mail-in voting restrictions. Why it matters: The ruling effectively freezes a key piece of Trump's attempted overhaul of mail-in voting. His executive order had enabled the USPS to refuse to deliver ballots to states that did not cooperate with the Postal Service on preventing what the administration has claimed is rampant voting by non-citizens. Flashback: Federal judge blocks Trump's mail-in voting order Editor's note: This is a breaking news story. Please check back for updates.