In the POLITICO Battleground States Polling Average for Iowa, Donald Trump holds a narrow advantage. | Getty Iowa poll: Trump expands lead over Clinton

Donald Trump has opened up an eight-point lead over Hillary Clinton in the battleground state of Iowa, according to a Monmouth University poll of likely voters released Thursday.

Matched against Clinton, as well as Libertarian nominee Gary Johnson and Green nominee Jill Stein, Trump received 45 percent support in the latest survey, up one point from his performance in the university’s last poll from the state conducted in July.

Approximately 37 percent said they would vote for Clinton, down from the 42 percent she received in the same poll two months ago. Johnson received 8 percent, while Stein followed with 2 percent. Another 2 percent said they would vote for another candidate, while 6 percent said they are undecided among those choices.

The Monmouth survey, conducted between Monday and Wednesday, is the latest indication of Trump’s momentum in swing-state and national polls, where he has eaten into or eclipsed Clinton’s cushy post-convention bounce. Separate polls released Wednesday showed Trump with at least a nominal advantage in Nevada, Ohio and Florida.

In the POLITICO Battleground States Polling Average for Iowa, Trump holds a narrow advantage of 42 percent to 40.6 percent, factoring in five different surveys conducted back to the second week of August.

Even as Trump’s standing in the ballot test has improved, Iowa voters’ general impression of Trump (55 percent unfavorable to 32 percent favorable) has actually gotten a little worse since July, when 51 percent said they saw him unfavorably, compared with 33 percent who said they had a generally favorable impression of him. Clinton’s favorability numbers decreased two points from July (from an already low 32 percent to 30 percent) while the share of those viewing her unfavorably rose by the same share (56 percent to 58 percent).

The same survey also found incumbent Republican Sen. Chuck Grassley pushing his advantage over Democratic challenger Patty Judge to 17 points—56 percent to 39 percent.

Grassley, as the chairman of the Senate Judiciary Committee, has been firm about no hearing for Supreme Court nominee Merrick Garland before the election. In the last Monmouth poll, Grassley led 52 percent to 42 percent.

The poll was conducted Sept. 12-14 via landlines and cellphones, surveying 401 likely voters with an overall margin of error of plus or minus 4.9 percentage points.