The revelation that American president Donald Trump conditioned military aid to Ukraine on the country opening an investigation into the business dealings of former vice president Joe Biden’s son there have renewed pressure on House speaker Nancy Pelosi to begin impeachment proceedings.

This is the textbook impeachable offense: using the power of the presidency to bribe or blackmail a foreign leader and conspiring with another country against your political opponents in the United States.

So what is Pelosi waiting for?

Public opinion

I’ve argued against blaming Pelosi for doing her job. Too many progressives believe that she, rather than the center-left majority in the Democratic caucus, is standing in the way of their priorities.

According to Jonathan Bernstein, that’s the speaker’s job: to take the brunt of abuse from her own party in order to protect its electorally most vulnerable members.

A majority of 137 out of 235 House Democrats (and one former Republican, Justin Amash) support impeachment. But one in two Americans still oppose it. The share of voters who favor impeaching Trump has consistently hovered around 35-38 percent.

There is something to be said for leadership. If the House were to initiate impeachment proceedings, and all the reasons for it — from Trump being willing to accept Russia’s help to win the 2016 election to ample evidence of corruption and nepotism in the White House — were in the news day after day, public opinion might change.

When the Watergate hearings started in May 1973, just one in five Americans wanted Richard Nixon out. As the hearings went on, and Nixon attempted to stonewall the inquiry, support for his impeachment grew. But it wasn’t until a year later, when the House formally recommended impeachment in July 1974, that a majority of Americans agreed the president had to go.

And that was at a time when party discipline was looser and there was no Fox News, and no online conservative echo chamber, to invent alternative facts and blame Democrats.

The right time

Pelosi’s job is to decide when the time is right. The worst thing that could happen is that Democrats try and fail to impeach Trump before the 2020 election. He would then undoubtedly claim vindication and portray Democrats as extremists. It might be better to wait a little while longer for public opinion to catch up with the facts and attempt impeachment in an election year.

Maybe she has waited long enough. Maybe she has waited too long already. Pelosi is not infallible. But let’s not be quick to assume that the most successful woman in American politics is making a mistake.