(CNN) Joe Biden has been officially running for president for less than a month. But in that short time, he has gone from nominal front-runner of a closely crowded pack of top-tier candidates to the clear frontrunner to be the party's 2020 nominee against Donald Trump.

Polling tells the story. Biden released a video on April 25 announcing he was running . Two days later, the Real Clear Politics average of national polling on the 2020 Democratic primary put Biden at 29% to 23% for Bernie Sanders, 8% for Kamala Harris and 7.5% for Pete Buttigieg.

Today's RCP polling average puts Biden at 39% to Sanders' 16%. No other candidate has double-digit support. The trend line on Biden is where it should be (although he has dipped somewhat from his average of 41% last week). While all candidates get some boost from the flush of media attention that comes from an official entry into the race, Biden's has been both a) bigger and b) longer than almost anyone expected.

What that surge has done is turn the race into Biden in a tier by himself and then a gaggle of candidates -- Sanders, Harris, Buttigieg and Elizabeth Warren -- on a second tier well below the former VP.

Biden and his team are doing everything they can to drive that perception, releasing presidential-looking daily schedules and having his events covered by a pool reporter. Biden, too, is limiting his public appearances to keep the chances of making a race-altering gaffe as low as possible.