[My view: With or without "leverage" in the Senate (to quibble over that term is moot), I personally believe the issue of whether there will be fair and open trial is gigantic and crucial, and that delivering the Articles should and must wait until that is explicitly clear and debated, then advanced in accordance with the satisfaction of the House leaders.]
Nancy Pelosi has been the most effective speaker of the House of the last few decades. But she has a more consistently excellent record in managing her caucus and counting votes than she does in shaping a public message. So I think it's reasonable to ask: What do she and House Democrats think they're doing right now?
They have paused the impeachment proceedings and said they might delay sending the charges against President Trump to the Senate. Democrats want assurances of a fair trial there.
The reality is that Democrats have little leverage.
Republicans hold a majority in the Senate and can design the trial however they want, so long as they stick together. There is no reason to think Pelosi's stall tactics will create division among them.
Yes, Trump wants to be acquitted. But there are also advantages for him and the Republicans if House Democrats never send the articles. Trump can brush off the impeachment as a botched process and portray the Democrats as weak. Swing voters may well agree with that assessment. And vulnerable Senate Republicans will be allowed to avoid tough impeachment votes. As Mitch McConnell, the Senate Republican leader, said yesterday, "I'm not sure what leverage there is" in holding back "something we do not want."
Most likely, Pelosi understands this and is merely trying to call attention to the Senate's refusal to hold a fair trial. If that's the case, she will send the articles to the Senate in short order. She has no good alternative. The only way to ensure a better functioning Senate is to win more elections in 2020.