With less than a week to go before voting begins in the Democratic presidential primary, Sen. Bernie Sanders (I-Vt.) is making gains in early states and national polls alike.

A slew of surveys released in recent days suggest that Sanders has caught up with former vice president Joe Biden in Iowa, which is poised to hold its caucuses next Monday, and has opened up a lead in New Hampshire, which votes the following week.

"Things are looking beautiful," said Ben Cohen, a national cochair of Sanders' presidential campaign. He and fellow Ben & Jerry's cofounder Jerry Greenfield have been spending the week crisscrossing Iowa to campaign for Sanders. "The people we've been talking to are incredibly enthusiastic," Cohen said.

Even as Sanders focuses on the early voting states of Iowa, New Hampshire, Nevada and South Carolina, his campaign has increased its investment in the 14 states that vote on March 3. On that day, better known as Super Tuesday, 1,344 delegates will be awarded — including 415 in California and 228 in Texas — compared with the 41 delegates out of Iowa.

A new poll released Tuesday by the Los Angeles Times shows Sanders leading the pack in California with 26 percent of the vote, followed by Sen. Elizabeth Warren (D-Mass.) with 20 percent and Biden with 15 percent. On the same day, the Sanders campaign announced that it was launching a $2.5 million ad campaign in California and Texas — a relatively small buy in such massive states but a sign of Sanders' ability to bankroll a long fight for delegates.

“It is thanks to our grassroots donors that we can make big investments in the vital states of California and Texas," Sanders campaign manager Faiz Shakir said in a written statement. "We have the strength and the enthusiasm to fund a campaign to not only win the Democratic nomination but to defeat Donald Trump and create a political revolution that transforms this country."

As the Iowa caucuses near, Sanders remains stuck in Washington, D.C., for a second week in a row, participating in the impeachment trial of President Donald Trump. Nevertheless, recent polls of the Hawkeye State indicate that the Vermonter is holding his own.

Three of the four most recent surveys show Sanders leading Biden by anywhere from 1 to 9 percentage points in the state, according to FiveThirtyEight, while the fourth shows Biden leading Sanders by 7 points. The site's forecasting model predicts that Sanders and Biden each have a 1 in 3 chance of prevailing in Iowa.

Sanders is doing even better in New Hampshire, which votes on February 11. All four of the most recent polls show him ahead by 5 to 12 percentage points there, according to FiveThirtyEight. Two of those polls found Biden in second place, while the other two had former mayor Pete Buttigieg of South Bend, Ind., in second. FiveThirtyEight's model predicts that Sanders has a 1 in 2 chance of winning his neighboring state.

Cohen attributes some of Sanders' strength to the passion of his staff and volunteers. "He's got incredibly motivated, enthusiastic supporters that are knocking on doors and making phone calls. You know, that's the thing that really makes the difference," he said. "Everybody can buy gobs of TV ads, but nothing is as important — nothing makes as much of an impression on a voter as talking to a real live human being."

With Sanders in D.C., Cohen said, campaign surrogates such as himself are engaged in a "full-court press" to make up for their leader's absence. "His whole theme has been, 'Not me, us,'" Cohen said, referring to the campaign slogan. "So us is doing everything we can right now."