On January 6, in a rambling speech, Trump said the following:
"Because if Mike Pence does the right thing, we win the election. All he has to do, all this is, this is from the number one, or certainly one of the top, Constitutional lawyers in our country. He has the absolute right to do it. We're supposed to protect our country, support our country, support our Constitution, and protect our constitution.
"States want to revote. The states got defrauded. They were given false information. They voted on it. Now they want to recertify. They want it back. All Vice President Pence has to do is send it back to the states to recertify and we become president and you are the happiest people.
"And I actually, I just spoke to Mike. I said: "Mike, that doesn't take courage. What takes courage is to do nothing. That takes courage." And then we're stuck with a president who lost the election by a lot and we have to live with that for four more years. We're just not going to let that happen."
Read all of that carefully: he is telling Mike Pence, his Vice President, to ignore his constitutional duty in the Senate on that day, and send the votes back to the states. That was not within his constitutional power to do, and therefore would have been an unlawful attempt to overturn the election. Pence didn't do that, but there is zero question that Donald Trump is telling him to do so.
The Constitution
directs the president of the Senate (the VP) to open the certificates of the election results from the states in the presence of the Senate and House and instructs that the votes
“shall then be counted,” said Garrett Epps, a professor of constitutional law at the University of Oregon. There is no suggestion of "unless he decides not to bother, and just send them back."