Donald Trump has been trailing Hillary Clinton in swing-state polls. | Getty More swing state polling blues for Trump

Hillary Clinton leads Donald Trump in three key battleground states, according to new polls released Tuesday — including a commanding advantage in vote-rich Pennsylvania.

The NBC News/Wall Street Journal/Marist polls, conducted last Wednesday through Sunday, show Clinton leading Trump by 4 points in Iowa (41 percent to 37 percent), 5 points in Ohio (43 percent to 38 percent) and 11 points in Pennsylvania (48 percent to 37 percent).

All three surveys show movement towards Clinton over the past month. In early July, Clinton led by 3 points in Iowa and 9 points in Pennsylvania; Clinton and Trump were tied in Ohio last month.

Clinton’s lead shrinks in subsequent poll questions that include Libertarian Party nominee Gary Johnson and Green Party nominee Jill Stein: On a four-way ballot, the two major party candidates were tied in Iowa, while Clinton had a 4-point edge in Ohio and a 9-point lead in Pennsylvania.

And even on the two-way ballot, there are warning signs for both candidates. In Iowa, 22 percent of registered voters said they were either undecided or backed neither candidate. In Ohio, 19 percent couldn’t choose between Clinton and Trump, while it was 15 percent on the sidelines in Pennsylvania.

But other measures underscore Clinton’s grip on the race. In two of the three states, Clinton’s lead actually swells among voters who say they will definitely turn out in November: Clinton leads Trump by 7 points in Iowa on the head-to-head ballot among definite voters, and by 15 points in Pennsylvania. (In Ohio, Clinton’s lead contracts slightly, from 5 points to 3 points, among definite voters.)

The results in Ohio and Pennsylvania closely track with Quinnipiac University polls released earlier Tuesday, which gave Clinton leads of 4 and 10 percentage points, respectively, among likely voters.

A yawning gender gap in each state favors Clinton. Trump leads among men by 10 points in Iowa, 1 point in Ohio and 4 points in Pennsylvania. But Clinton swamps Trump with large advantages among female voters: 17 points in Iowa, 10 points in Ohio and 25 points in Pennsylvania.

In Ohio and Pennsylvania, Clinton is also bolstered by African-American voters. In both states, Trump is at only 1 percent among black voters. (Too few black voters live in Iowa for pollsters to estimate their attitudes).

Clinton is also benefiting from greater party unity in all three states. She’s winning more Democrats in each state — 88 percent in Iowa, 87 percent in Ohio and 91 percent in Pennsylvania — than Trump is winning Republicans (83 percent in both Iowa and Ohio, and just 77 percent in Pennsylvania).

One bright spot for Republicans: Incumbent GOP senators in Iowa and Ohio lead their GOP challengers. In Iowa, six-term Sen. Chuck Grassley has a 10-point lead over Democrat Patty Judge, 52 percent to 42 percent. In Ohio, first-term Sen. Rob Portman’s lead over former Gov. Ted Strickland stands at 5 points, 48 percent to 43 percent.

But in Pennsylvania, Democrat Katie McGinty has a slight edge over GOP Sen. Pat Toomey, 48 percent to 44 percent.

And, just like in the presidential race, a potential turnout disparity is threatening Republicans. In each state, Democrats are running stronger among those voters who say they will definitely turn out in November than among the broader pool of registered voters. In Iowa, Grassley’s lead disappears among definite voters: He’s left with just a 1-point advantage over Judge, 48 percent to 47 percent.

In Ohio, Portman’s edge over Strickland contracts from 5 points to 3 points. And in Pennsylvania, McGinty’s lead grows from 4 points to 7 points among definite voters.

The NBC News/Wall Street Journal/Marist polls surveyed 899 registered voters in Iowa, 889 registered voters in Ohio and 834 registered voters in Pennsylvania. The margins of error are plus or minus 3.3 percentage points in Iowa and Ohio, and 3.4 percentage points in Pennsylvania.