Yes, they absolutely need Republicans -- not only to adopt the articles of impeachment in the House and to convict in the Senate, but also for the credibility of the process.  During the 2016 campaign I said that I believed that the election of Donald Trump would lead to the worst Constitutional crisis since the Civil War.  I did not think that it would come so soon.  The onus is on the Republicans: Do they love the country more than their party? I would think that doing the right thing might be a little easier for them: removing Trump will give them a Republican president; there hasn't been one since George W. Bush left office in 2009.