WASHINGTON — Financial markets were watching, the retirement accounts of millions of Americans on the line.

Nervous senators were watching too, well aware that political fortunes could be on the line.

So for perhaps the most important vote of the year, the Senate did something extraordinary this week: It tried to keep the vote tally secret until the outcome was assured.

As lawmakers voted Wednesday on must-pass legislation to increase the government’s debt limit, they dropped the parliamentary equivalent of a curtain on the voting as it was in progress.

Typically, roll-call votes in the Senate play out in a very public manner. People watching from the galleries or tracking action via C-SPAN can watch democracy unfold in all its messy wonder.

Each senator’s vote is announced by the clerk; each time a senator switches sides, that’s announced too. Onlookers can keep a running tally of how it’s going.

But not this time. Fifteen minutes into the vote, as captured by C-Span cameras, the tally clerk rose to recite the vote. A Senate aide alerted Sen. John McCain, R-Ariz., one of the six Republicans who later switched his vote from “nay” to “aye.” McCain intervened, and the clerk sat right back down. “Would you ...” McCain said before the live microphone cut off.

A McCain spokesman denied the Arizonan intervened. “McCain didn’t know that they weren’t going to read the names and he didn’t care if they did. He didn’t have input on that,” e-mailed spokesman Brian Rogers.

Senate leaders hoped they would get the necessary votes ultimately, but they were worried at the time and faced financial and political repercussions if the vote cratered in public view.

Both sides were concerned that investors might panic, causing the stock market to tank in real time. That’s what happened in 2008 when the House voted to reject a Wall Street bailout plan, triggering a 7 percent drop in the Dow Jones Industrial Average.

“We were very disappointed that Wednesday’s change in Senate voting protocol kept us from giving the public real time access to this key vote,” said Terry Murphy, C-SPAN’s vice president of programming. “The tactic certainly gives the concept of legislative transparency a black eye.”

Afterward, there was confusion. Initially, a spokesman for Majority Leader Harry Reid, the Nevada Democrat who runs the Senate, said Reid was unaware at the time that Senate procedures were being bypassed. Later, spokesman Adam Jentleson said Reid “consented to Republicans’ request.”

While acknowledging the media’s concerns had merit, Jentleson couldn’t guarantee a veiled vote won’t happen again.