WASHINGTON — It’s been easy for majority Democrats to keep Republicans from shifting the focus of the House impeachment hearings. Yet GOP leverage to do just that will grow should the battle reach the Republican-run Senate.

If the House votes to impeach President Donald Trump, which seems likely, the Senate would hold a trial on whether to oust him from office, probably early next year.

There, attorneys for Trump, along with Senate Majority Leader Mitch McConnell, R-Ky., or any other senator can call their own witnesses. The big catch is they’d need enough votes from the 53 GOP senators to muster a majority and prevent Democrats from blocking them.

Assuming Republican senators stay united, which isn’t guaranteed, Trump’s defenders could try refocusing the inquiry by seeking testimony from people like Hunter Biden, son of 2020 Democratic presidential hopeful Joe Biden.

Trump and some Republicans have pushed an unsubstantiated narrative suggesting improprieties by Hunter Biden when he worked for Burisma, a Ukrainian natural gas company, while his father was vice president.

Calling witnesses about that — and another unfounded theory about Ukrainian involvement in the 2016 presidential election — could make life difficult for Joe Biden just as his party’s presidential primary season is beginning.

It would also please the GOP’s core conservative voters, woo some independents and perhaps help any wavering Republican senators stand by Trump on climactic votes over whether to remove him from office.

“What Republicans want to do is broaden the story,” said David Hoppe, who was chief of staff to Senate Majority Leader Trent Lott, R-Miss., during the 1999 impeachment trial of President Bill Clinton.

But calling such witnesses could be viewed as a blatantly political move that overreaches, risking voter backlash in next November’s elections. That might be especially damaging for moderate Republicans facing tough reelections in swing states, where centrist voters could be pivotal.