WASHINGTON — Before the House voted on Thursday to endorse the Democratic-led impeachment inquiry into President Trump, two of the most conservative lawmakers in the caucus hazarded a guess as to whether some colleagues might join them in opposing the measure.

“It might just be us,” they said.

In the end, they were right. Democrats on Thursday linked arms and took the plunge into the impeachment pool, as Republicans unanimously opposed the resolution in a 232-to-196 vote. Left on the sidelines were Representative Jeff Van Drew of New Jersey and Representative Collin C. Peterson of Minnesota, both known as consistent, conservative thorns in their party’s side.

Their votes did not come as much of a surprise to Democrats, the vast majority of whom rapidly coalesced behind the resolution that ushered in a new public phase of the process. Both men had publicly aired their concerns that impeachment would be divisive and fruitless.

“I don’t want to move the country further apart,” Mr. Van Drew told reporters after casting his vote. “We could investigate the issues that we’re really concerned about without going further down the impeachment road.”