As Hillary Clinton's lead in the polls continues to fall, her attacks on Bernie Sanders have stepped up. (Peter Stevenson/The Washington Post)

For much of the 2016 presidential campaign, Hillary Clinton has been considered the presumptive Democratic nominee. Her challengers were few and far between, her poll numbers were rock-solid, and even Republicans seemed to think she had the nomination in the bag.

Recent polling, though, has made it clear that Bernie Sanders is catching up to her in Iowa, New Hampshire, and nationally (although, as The Fix’s Philip Bump notes, variations in polling methodology and sampling can make those swings look more dramatic, day-to-day, than they probably are).

There’s no question that Clinton’s rhetoric on Sanders has changed. Gone is the cordiality seen when the two smiled and shook hands after Sanders told the world that “the American people are sick and tired of hearing about (Clinton’s) damn emails.” And while Clinton spent much of her time at her early rallies discussing her differences with Republicans, she's now added Sanders into the mix.

The former secretary of state tore into Sanders during a rally Thursday in Indianola, Iowa, saying she’s “not interested in ideas that sound good on paper but will never make it in the real world.” She’s not the only one to critique the democratic socialist Sanders on that count; Sanders has repeatedly been asked how he would push his ideas through a hostile Congress that is all but sure to remain in GOP control for the foreseeable future.

And she sharpened her attacks on Sanders’s foreign policy credentials. While he did better on foreign policy in the most recent debate, Sanders’s early debate performances earned him criticism for turning most questions back to his central argument about wealth inequality, Wall Street and big banks. Thursday, Clinton echoed that sentiment, saying on foreign policy, “sometimes it can sound like he hasn’t really thought it through.”

That comes on top of a debate performance on Sunday in which Clinton laid out the central difference between the two: While Clinton frames her candidacy as a continuation of President Obama’s policies, Sanders wants a “revolution.” And Clinton pounced on him for that, casting him as the anti-Obama.

Clinton’s attacks on Sanders have become sharper and more frequent as the gap in their polling numbers closes. Only 10 days from the Iowa caucuses, Team Clinton hopes those attacks are enough to maintain any kind of lead she has left.