I'd like to add that it's fine to try to resend before it doesn't show on block explorers. I made transaction in December which remained unconfirmed for over 21 days. It still showed on blocktrail, blockchain.info and a few others that I checked, but Trezor let me create a new transaction where I used a proper fee. Despite the transactions showing, it got broadcast successfully and confirmed in the next block.
I don't believe Electrum tries to rebroadcast automatically - you have to click a button for that.