Euchre partner leads with trump - why?
Your partner should ALWAYS lead trump to your call in third chair. The failure of so many online players to do this reflects a lack of understanding of the game.

If you called it with the Right, then their low trump effectively gives the maker the lead and control of the hand.

If you called without the Right, then your partner is helping flush the top trump cards out of your opponents' hands.

If your partner leads high trump then he's helpfully showing you where it is so you know your cards are boss.

*IF YOU CALL TRUMP IN THIRD CHAIR THEN YOU SHOULD BE LEADING IT, and you should probably be leading it in every other chair too. So many hands are misplayed for failure to do this, so many times you get euchred when you could have dropped both of your opponents' bauers on trick one with a small Trump lead.

For more, read this column by the respected Natty Bumppo.